17 research outputs found
Wet chemical passivation of interface defects in a a SI H c Si heterojunction solar cells with randomly distributed pyramids
No full textWET CHEMICAL PASSIVATION OF INTERFACE DEFECTS IN a SI H c SI HETEROJUNCTION SOLAR CELLS WITH RANDOMLY DISTRIBUTED PYRAMIDS H. Angermann, J. Rappich, K. v. Maydell, E. Conrad, I. Sieber, D. Schaffarzik and M. Schmidt Hahn Meitner Institut Berlin, Kekul str.5, D 12489 Berlin Corresponding author H. Angermann, Hahn Meitner Institut Berlin HMI , Kekul str.5, D 12489 Berlin, Tel 49 30 8062 1368, Fax 49 30 8062 1333 e mail angermann helmholtz berlin.de ABSTRACT Two non destructive, very surface sensitive tech niques, the large signal field modulated surface photovoltage SPV method and pulsed photoluminescence spectroscopy PL were applied to investigate both wet chemically treated substrate surfaces and a Si c Si interfaces. In order to prepare silicon substrates with randomly distributed pyramids without surface micro roughness and native oxide contamination and to passivate them during the technological process, we investigated special combinations of wet chemical etching and cleaning procedures. Compared to conventional pre treatments, significantly lower densities surface states and recombination loss were achieved on silicon substrates textured with randomly distributed upside pyramids and on the resulting a Si c Si in terfaces after deposition. It was shown that the open circuit voltage Voc and solar cell efficiency of TCO a Si H n c Si p Al solar cells are mainly influence by the preparation induced morphology and electronic properties of substrate surface. Keywords silicon substrates, defect density, wet chemical pretreatmen
Mechanism of the inhibition of Ca2+-activated Cl- currents by phosphorylation in pulmonary arterial smooth muscle cells
No full textA radiation and propagation problem for a Helmholtz equation with a compactly supported nonlinearity
No full textThe present work describes some extensions of an approach, originally
developed by V.V. Yatsyk and the author, for the theoretical and numerical
analysis of scattering and radiation effects on infinite plates with cubically
polarized layers. The new aspects lie on the transition to more generally
shaped, two- or three-dimensional objects, which no longer necessarily have to
be represented in terms a Cartesian product of real intervals, to more general
nonlinearities (including saturation) and the possibility of an efficient
numerical approximation of the electromagnetic fields and derived quantities
(such as energy, transmission coefficient, etc.). The paper advocates an
approach that consists in transforming the original full-space problem for a
nonlinear Helmholtz equation (as the simplest model) into an equivalent
boundary-value problem on a bounded domain by means of a nonlocal
Dirichlet-to-Neumann (DtN) operator. It is shown that the transformed problem
is equivalent to the original one and can be solved uniquely under suitable
conditions. Morever, the impact of the truncation of the DtN operator on the
resulting solution is investigated, so that the way to the numerical solution
by appropriate finite element methods is available
Investigation of Acute Pulmonary Deficits Associated with Biomass Fuel Cookstove Emissions in Rural Bangladesh
No full textThe use of solid biomass fuels in cookstoves has been associated with chronic health impacts that disproportionately affect women worldwide. Solid fuel stoves that use wood, plant matter, and cow dung are commonly used for household cooking in rural Bangladesh. This study investigates the immediate effects of acute elevated cookstove emission exposures on pulmonary function. Pulmonary function was measured with spirometry before and during cooking to assess changes in respiratory function during exposure to cookstove emissions for 15 females ages 18–65. Cookstove emissions were characterized using continuous measurements of particulate matter (PM2.5—aerodynamic diameter <2.5 μm) concentrations at a 1 s time resolution for each household. Several case studies were observed where women ≥40 years who had been cooking for ≥25 years suffered from severe pulmonary impairment. Forced expiratory volume in one second over forced vital capacity (FEV1/FVC) was found to moderately decline (p = 0.06) during cooking versus non-cooking in the study cohort. The study found a significant (α < 0.05) negative association between 3- and 10-min maximum PM2.5 emissions during cooking and lung function measurements of forced vital capacity (FVC), forced expiratory volume in one second (FEV1), and FEV1/FVC obtained during cooking intervals. This study found that exposure to biomass burning emissions from solid fuel stoves- associated with acute elevated PM2.5 concentrations- leads to a decrease in pulmonary function, although further research is needed to ascertain the prolonged (e.g., daily, for multiple years) impacts of acute PM2.5 exposure on immediate and sustained respiratory impairment
Arsenic Methylation Capacity and Metabolic Syndrome in the 2013–2014 U.S. National Health and Nutrition Examination Survey (NHANES)
No full textArsenic methylation capacity is associated with metabolic syndrome and its components among highly exposed populations. However, this association has not been investigated in low to moderately exposed populations. Therefore, we investigated arsenic methylation capacity in relation to the clinical diagnosis of metabolic syndrome in a low arsenic exposure population. Additionally, we compared arsenic methylation patterns present in our sample to those of more highly exposed populations. Using logistic regression models adjusted for relevant biological and lifestyle covariates, we report no association between increased arsenic methylation and metabolic syndrome in a population in which arsenic is regulated at 10 ppb in drinking water. However, we cannot rule out the possibility of a positive association between arsenic methylation and metabolic syndrome in a subsample of women with normal body mass index (BMI). To our knowledge this is the first investigation of arsenic methylation capacity with respect to metabolic syndrome in a low exposure population. We also report that methylation patterns in our sample are similar to those found in highly exposed populations. Additionally, we report that gender and BMI significantly modify the effect of arsenic methylation on metabolic syndrome. Future studies should evaluate the effectiveness of arsenic policy enforcement on subclinical biomarkers of cardiovascular disease
Antioxidants Protect against Arsenic Induced Mitochondrial Cardio-Toxicity
No full textArsenic is a potent cardiovascular toxicant associated with numerous biomarkers of cardiovascular diseases in exposed human populations. Arsenic is also a carcinogen, yet arsenic trioxide is used as a therapeutic agent in the treatment of acute promyelotic leukemia (APL). The therapeutic use of arsenic is limited due to its severe cardiovascular side effects. Many of the toxic effects of arsenic are mediated by mitochondrial dysfunction and related to arsenic’s effect on oxidative stress. Therefore, we investigated the effectiveness of antioxidants against arsenic induced cardiovascular dysfunction. A growing body of evidence suggests that antioxidant phytonutrients may ameliorate the toxic effects of arsenic on mitochondria by scavenging free radicals. This review identifies 21 antioxidants that can effectively reverse mitochondrial dysfunction and oxidative stress in cardiovascular cells and tissues. In addition, we propose that antioxidants have the potential to improve the cardiovascular health of millions of people chronically exposed to elevated arsenic concentrations through contaminated water supplies or used to treat certain types of leukemias. Importantly, we identify conceptual gaps in research and development of new mito-protective antioxidants and suggest avenues for future research to improve bioavailability of antioxidants and distribution to target tissues in order reduce arsenic-induced cardiovascular toxicity in a real-world context
Aldehydes in Exhaled Breath during E-Cigarette Vaping: Pilot Study Results
No full textSeveral studies have shown the presence of aldehydes (i.e., formaldehyde, acrolein) in mainstream emissions of some e-cigarettes. For this reason, concerns have been raised regarding potential toxicity. The purpose of this research was to measure levels of carbonyls in exhaled breath of e-cigarette users during “vaping” sessions and estimate the respiratory tract (RT) uptake of specific aldehydes, including formaldehyde and acetaldehyde. We measured concentrations of 12 carbonyls in e-cigarette aerosols produced directly by e-cigarettes and in the exhaled breath of 12 participants (19 sessions). Carbonyls were sampled on 2,4-dinitrophenylhydrazine (DNPH) cartridges and analyzed with high performance liquid chromatography (HPLC) coupled with a UV/Vis photodiode detector. We found that in most cases, levels of aldehydes and methyl ethyl ketone (MEK) were significantly higher (2–125 times) in exhaled e-cigarette breaths than in pre-exposed breath. Exposure levels for the most abundant individual carbonyls in e-cigarette emissions—formaldehyde, acetaldehyde, acrolein—were between the limit of quantification (LOQ) and 24.4 μg·puff−1. The mean retention of formaldehyde in the respiratory tract was 99.7 ± 0.9% for all participants, while acetaldehyde retention was 91.6 ± 9.9%. Within the limitation of a small number of participants, our results showed that there is an increase in breath carbonyls during e-cigarette use
Development and optimization of a Si H c Si heterojunction solar cells completely processed at low temperatures
No full textSubject Number 2 Crystalline Silicon Solar Cells and Materials Technology Development and optimization of a Si H c Si heterojunction solar cells completely processed at low temperatures K. v. Maydell, E. Conrad, H. Angermann, C. Schubert, R. Stangl and M. Schmidt Hahn Meitner Institut Berlin, Kekul str.5, D 12489 Berlin Corresponding author K. v. Maydell, Hahn Meitner Institut Berlin HMI , Kekul str.5, D 12489 Berlin, Tel 49 30 8062 1350, Fax 49 30 8062 1333 e mail maydell helmholtz berlin.de We report on the development and optimization of amorphous crystalline silicon a Si H c Si solar cells which where completely processed at temperatures below 230 C. Both doping sequences were investigated a Si H n c Si p and a Si H p c Si n . No intrinsic buffer layers between the a Si H and the c Si wafer were used. To reach high efficiencies a low temperature a Si H rear side has been developed. Using surface photovoltage measurements it can be shown that a highly doped a Si H layer causes the formation of a back surface field at the rear side of the wafer. A simulation study, using our simulation program AFORS HET, shows that the potential of the efficiency of this kind of solar cells is larger 23 using the measured defect characteristics of the a Si H layers. The most dominating loss mechanism is recombination at the interface. The highest efficiencies obtained so far are 17.4 on p type and 18.2 on n type substrates. For reaching efficiencies towards 20 the interface states density of the a Si H c Si heterojunction on the front and back side has to be minimized or their incorporation into the recombination process has to be suppressed. Especially for textured substrates this is most important since VOC is reduced by about 20 mV compared to polished substrates. This can be done by different ways I Using appropriate preconditioning of the wafer, the surface states density can be reduced which results in a low interface states density of the resulting heterojunction. II The growth conditions of the a Si H layer on the c Si wafer have to be optimized in order to reduce the interface states density. We report on two different preconditioning methods prior to the a Si H deposition Hydrogen plasma passivation and wet chemical treatment of the c Si wafer. A H plasma passivation leads to a reduction in the effective recombination at the a Si H c Si interface as shown by transient surface photovoltage measurements. This causes an enhancement in the solar cells open circuit voltage up to 30mV on textured substrates. The standard wafer cleaning sequence is composed of a RCA cleaning followed by an HF dip. This usually leads to a rough surface in atomic scale. We tried to smoothen the surface using an additional wet chemical process step. This causes a reduction in the surface states density of the c Si wafer, a decrease of recombination at the a Si H c Si interface and thus to an enhancement in VOC. We will present the results of a Si H c Si solar cells on n type and p type c Si wafers with the combination of optimized wet chemical and H plasma pre treatments and a Si H deposition conditions
Intricate Interaction Between Store-Operated Calcium Entry and Calcium-Activated Chloride Channels in Pulmonary Artery Smooth Muscle Cells
No full textLe premier livre sur les techniques de construction en suédois : compilation ou création ?
No full textParu en 1752, Inledning till Mecaniken och Byggningskonsten jämte en beskrifning öfwer åtskillige af framledne coimmercie-rådet och commendeuren af kongl. Nordstierne-Orden Hr. Polhem opfundne machiner par Carl Henric König (1726-1804) constitue le premier ouvrage publié en suédois sur l’art de la construction et de la mécanique. La rédaction de cet ouvrage eut lieu sous la supervision d’Augustin Ehrensvärd (ingénieur en charge de fortifications) et probablement en collaboration avec Johan E. Carlberg (architecte de la ville de Stockholm). Commencé en 1744 l’idée initiale était de réaliser un inventaire des inventions de Christopher Polhem (1661-1751), mais dans sa version finale l’introduction prit la forme d’un manuel sur l’art de la construction. En effet, il semble que ce livre fut composé pour servir de support dans l’enseignement à l’école d’architecture de la ville de Stockholm où König enseigna à partir de 1745. En 1773 l’auteur obtint le titre d’architecte de la ville de Stockholm et l’année suivante il fut nommé professeur d’architecture à l’Académie royale des Beaux-Arts de Suède et fut le premier à y dispenser un cours sur ce sujet. La Bibliothèque royale conserve des manuscrits relatifs à cet enseignement. L’ouvrage est une compilation d’informations provenant d’ouvrages européens (tels Johann G. Angermann, l’abbé Laugier, Jacques François Blondel et Johann B. Izzo) ainsi qu’un résumé de l’art de la mécanique, tel qu’il fut appréhendé par Polhem et ses disciples.Published in 1752, Inledning till Mecaniken och Byggningskonsten jämte en beskrifning öfwer åtskillige af framledne coimmercie-rådet och commendeuren af kongl. Nordstierne-Orden Hr. Polhem opfundne machiner by Carl Henric König (1726-1804), constitutes the first book in Swedish on building and mechanics. Augustin Ehrenswärd (an engineer at the fortification) oversaw the writing of the book, and the author most probably also did collaborate with the city architect of Stockholm Johan E. Carlberg. Starting in 1744, the initial idea seems to have been to inventory the inventions by Christopher Polhem (1661-1751), but in its final version it turned out as a handbook on the arts of building. Actually, the book seems to have been conceived as a support for the school of architecture of Stockholm where König taught since 1745. In 1773, the author became himself city architect of Stockholm and the forthcoming year he was named Professor of architecture at the Swedish Royal Academy of Fine Arts and became the first lecturer on this subject. The Royal Library also holds manuscripts that were used to his teaching. The published book summarizes information from European literature on the subject (such as Johann G. Angermann, the abbé Laugier, Jacques François Blondel and Johann B. Izzo) as well as a summary of the art of mechanics by the Polhem and his students of the art of Mechanics
