Visualizing the performance loss of solar cells by IR thermography — an evaluation study on CIGS with artificially induced defects

Local electric defects may result in considerable performance losses in solar cells. Infrared (IR) thermography is one important tool to detect these defects on photovoltaic modules. Qualitative interpretation of IR images has been carried out successfully, but quantitative interpretation has been hampered by the lack of “calibration” defects. The aims of this study are to (i) establish methods to induce well‐defined electric defects in thin‐film solar cells serving as “calibration” defects and to (ii) assess the accuracy of IR imaging methods by using these artificially induced defects. This approach paves the way for improving quality control methods based on imaging in photovoltaic. We created ohmic defects (“shunts”) by using a focused ion beam and weak diodes (“interface shunts”) by applying a femto‐second laser at rather low power on copper indium gallium selenide cells. The defects can be induced precisely and reproducibly, and the severity of the defects on the electrical performance can be well adjusted by focused ion beam/laser parameters. The successive assessment of the IR measurement (ILIT‐Voc) revealed that this method can predict the losses in P_mpp (maximal power extractable) with a mean error of below 10%. Copyright © 2016 John Wiley & Sons, Ltd.     

Neueste Entwicklungen beim baulichen Brandschutz von Straßentunneln

In der jüngeren Vergangenheit hat sich gezeigt, dass Straßen tunnel durch größere Brände in erheblichem Umfang geschädigt werden können. In der Folge wurden verschiedene internationale Forschungsprojekte durchgeführt, um den baulichen Brandschutz von Straßentunneln weiterzuentwickeln. Aufbauend auf den internationalen Forschungsprojekten wurden vom BMVBS und der BASt drei nationale Forschungsprojekte zum baulichen Brandschutz von Straßentunneln initiiert. In diesen Projekten wurden vorhandene Temperatur‐Zeit‐Verläufe (sog. “Brandkurven”) für Straßentunnel, Brandver suche in Tunneln und reale Brände in Straßentunneln im Hinblick auf eine mögliche Anwendung zur Bemessung des baulichen Brandschutzes von Straßentunneln analysiert. Außerdem wurden die Temperatureindringung in die Tunnelinnenschale und die Tragfähigkeit von üblichen Tunnelquerschnitten infolge Brandeinwirkung numerisch ermittelt. Schließlich wurde anhand von Brandversuchen an großmaßstäblichen Probekörpern die Wirkung von PP‐Faserbeton auf das Abplatzverhalten von Innenschalenbeton untersucht. Über das Vorgehen und die Ergebnisse dieser Forschungsprojekte wird im Folgenden berichtet. Latest developments for structural fire protection of road tunnels. In the recent past it was shown that road tunnels can be damaged severely by large fires. For that reason several international research projects were carried out for further development of structural fire protection of road tunnels. Based on international research projects three national research projects were initiated by the Federal Ministry of Transport, Building and Urban Development (BMVBS) and the Federal Highway Research Institute (BASt). In the course of these projects existing temperature‐time‐progressions (so called ”fire curves”) for road tunnels, fire tests in tunnels and real fires in road tunnels were analyzed with regard to a possible application for the design of structural fire protection of road tunnels. Furthermore the temperature penetration in the tunnel lining and the load bearing capacity of usual tunnel sections were numerically examined under fire influence. Finally the influence of fiber‐modified concrete on the effect of explosive spalling was investigated by means of large scale fire tests on specimens made of concrete for tunnel lining. In the following procedures and results of the national research projects are described.     

Cell‐Selective,Apoptosis‐inducing Rhodium(III) Crown Thiaether Complexes

Half‐sandwich rhodium(III) polypyridyl (pp) complexes with the metal atom capped by the facial crown thiaether 1,4,7‐trithiacyclononane [9]aneS₃ represent a promising class of apoptosis‐inducing potent cytostatic agents. The necrotic damage caused by the complexes is negligible. In vitro cytotoxicity assays with the human cancer cell lines MCF‐7 and HT‐29 and immortalized HEK‐293 cells indicate that the dicationic κ²N(imino) complexes [([9]aneS₃)RhCl(pp)]²⁺ are much more active than monocationic complexes [([9]aneS₃)RhCl₂(L)]⁺ (L=imidazole, CH₃CN). Whereas the κ²N(amino) complex [([9]aneS₃)RhCl(piperazine)]²⁺ is inactive, replacing piperazine with the structurally analogous κ²S (thiaether) ligand 1,4‐dithiane restores cytotoxicity as evidenced by IC₅₀ values in the range 8.1‐11.6 μM . Spectroscopic (CD, UV/Vis, NOESY) and viscosity measurements indicate that the active dppz complex 8 (IC₅₀ values: 4.7–8.9 μM ) exhibits strong intercalative binding towards DNA whereas the even more potent bipyrimidine complex 9 (IC₅₀ values: 0.6–1.9 μM ) causes no alteration of the duplex B conformation. Weaker intercalative binding is observed for the dpq complex 7 . A comparative annexin V–propidium iodide binding assay with lymphoma (BJAB) cells and healthy leukocytes demonstrates that the cytotoxic activity of complex 8 and particularly complex 9 is highly selective towards the malignant cells.     

Concentration and distribution of heavy metals in urban airborne particulate matter in Frankfurt am Main, Germany

Heavy metal concentrations were measured in airborne dust collected at three sites with different traffic densities from August 2001 to July 2002 in the Frankfurt am Main area. Bulk samples of particulate matter (PM) with an aerodynamic equivalent diameter of <22 microm were collected on cellulose nitrate filters using air filtration devices. Fractionated samples of PM with an aerodynamic equivalent diameter of <10 microm were collected using an eight-stage Andersen impactor. Pb, Cd, Mn, Ni, Zn, V, As, Sb, Cu, Cr, Co, and Ce were determined by inductively coupled plasma sector field mass spectrometry, Pt and Rh were determined by adsorptive voltammetry, and Pd was determined by total reflection X-ray fluorescence analysis. The results show that the highest airborne heavy metal concentrations occurred at the main street with a large volume of traffic. With the exception of Co, V, Ce, and Mn, the heavy metals had an elevated enrichment factor compared to their concentrations in the continental crust. The main street site was especially contaminated with Sb, Zn, Cu, V, and Ni. Motor vehicles are the likely source of emissions. With the exception of Cr, Cu, and Zn, most of the airborne heavy metal concentrations determined for impactor samples deviate slightly from the results for total airborne dust. Heavy metal particle size distributions can be divided into three groups. For metals such as As, Cd, Pb, and V, the main fraction can be found in fine particles with a diameter of <2.1 microm, whereas Ce, Cr, Co, and Ni occur mainly in coarse particles with a diameter of >2.1 microm. Cu, Mn, Sb, Zn, Pt, Pd, and Rh occur in high concentrations in the medium range of the impactor stages (particle diameters of 1.1-4.7 microm). Metal concentrations in fine dust particles are needed to assess the human health risks of their inhalation.     

Eine Stellungnahme zum Beitrag von Sass & Treskatis: “Herstellungs- und Bemessungsgrundlagen für einen verlaufsgesteuerten Trinkwasserbrunnen ...”

Ohne Zusammenfassung Eingang des Beitrages: 14.03.2000 / Eingang des überarbeiteten Beitrages: nicht überarbeitet, nur korrigiert     

n-Type Doping of Vapor–Liquid–Solid Grown GaAs Nanowires

In this letter, n-type doping of GaAs nanowires grown by metal–organic vapor phase epitaxy in the vapor–liquid–solid growth mode on (111)B GaAs substrates is reported. A low growth temperature of 400°C is adjusted in order to exclude shell growth. The impact of doping precursors on the morphology of GaAs nanowires was investigated. Tetraethyl tin as doping precursor enables heavily n-type doped GaAs nanowires in a relatively small process window while no doping effect could be found for ditertiarybutylsilane. Electrical measurements carried out on single nanowires reveal an axially non-uniform doping profile. Within a number of wires from the same run, the donor concentrations N _D of GaAs nanowires are found to vary from 7 × 10¹⁷ cm^-3 to 2 × 10¹⁸ cm^-3. The n-type conductivity is proven by the transfer characteristics of fabricated nanowire metal–insulator-semiconductor field-effect transistor devices.     

Behavior of tissue-engineered human cartilage after transplantation into nude mice

Cartilage lacks the ability to regenerate structural defects. Therefore, autologous grafting has been used routinely to replace cartilaginous lesions. Because tissue engineering of human cartilage with the help of bioresorbable polymer scaffolds is possible in experimental models, the demand for the clinical application grows. In this study we present an analysis of the behavior of transplants made of human chondrocyte pools, agarose and the resorbable polymer scaffold Ethisorb and a preliminary comparison with transplants made of single patients' cells and Ethisorb but without the additional ingredient agarose. Chondrocytes were isolated from the matrix of human septal cartilage by enzymatic digestion. The pool cells were kept in monolayer culture for 2 weeks, the single patients' cells for 3–4 weeks. Chondrocyte pools were suspended in agarose and seeded into the resorbable polymer scaffold Ethisorb. Single patients' cells were seeded without agarose. All cell–polymer constructs were kept in perfusion culture for 10–14 days and transplanted subcutaneously into thymusaplastic nude mice. Additionally we implanted Ethisorb fleeces embedded in agarose without chondrocytes. After 6, 12 and 24 weeks the animals were sacrificed and the specimens were explanted and analyzed histochemically and immunohistochemically. Polymer scaffolds not seeded with chondrocytes did not show cartilage formation. Resorption was complete after 12 weeks in vivo. Transplants from cell pools remained mechanically stable over 24 weeks apart from four transplants that were resorbed completely. Cartilage formation was observed in all pool-specimens with the presence of chondronic structures and a homogeneous matrix containing hyaline cartilage-specific matrix molecules such as collagen type II. Single patients' transplants showed hyaline cartilage matrix synthesis and mechanical stability as well. Chondrocyte pools are a suitable method to study cartilage engineering of human cells in vitro and in vivo in experimental models. Under clinical conditions it is, however, necessary to study the generation of cartilage from single patients' cells. We showed that it is possible without additional ingredients such as agarose. However, variations in the preliminary results show that the clinical application with human cells is more difficult than one would expect when using human chondrocyte pools. Further studies need to be performed to find out which individual factors influence the in vitro engineered cartilage's fate in vivo. © 1999 Kluwer Academic Publishers     

Modelling of the borehole filling of double U-pipe heat exchangers

A new model MISOS is proposed for the simulation of the borehole filling (grout) of double U-pipe heat exchangers. When simulating ground-coupled heat pumps, a suitable model of the filling is necessary because the temperature of the filling effects the temperature of the heat carrier fluid. The filling is divided into three elements whose geometry corresponds to the different temperature zones. For each time step, the temperatures of the filling elements can be calculated from energy balances. MISOS is very fast compared to computational fluid dynamics (CFD) algorithms. CFD calculations were performed for different shank spacings, and results compared with those obtained from MISOS. If the pipe shanks are situated between the axis and the wall of the borehole, nearly the same difference of the fluid temperature between inlet and outlet is predicted by MISOS and CFD. For a minimal shank spacing, heating is overpredicted by about 6% for an extraction period of 3 h while an underprediction of about 9% is obtained for maximal shank spacing.     

Correlation between polyethylene topology and melt flow instabilities by determining in-situ pressure fluctuations and applying advanced data analysis

Using three high sensitive pressure transducers located inside a slit-die of a capillary rheometer and applying a set of advanced mathematical tools to process the acquired time dependent pressure signals, we are able to detect in-situ pressure fluctuations associated with sharkskin instabilities. Other distortions, as spurt and gross melt fracture, can also be in-situ detected. This originates from a factor of 10³ and 10² improvement in terms of time and pressure resolution achieved using the new set-up and data analysis that it will be described in detail in this article. Our approach quantifies the effect of polymer topology and shear rate on the characteristic frequency and amplitude of these pressure fluctuations inside the die. Depending on the polymer structure and the shear rate, different instabilities with large deviation in their main properties at melt-state, can be determined. Based on our results, a polymer-independent power law relationship between the characteristic frequency of the instability and the apparent shear stress has been found. Combining this new technique with the advanced mathematical analysis used, clear evidences concerning the origin and location of these instabilities, could be established. According to our analysis, the spurt instability starts in the entrance of the die and it propagates downstream while increasing its velocity along the die. This was confirmed by non-zero-time-lags in the cross-correlation function between the transducers located inside the slit-die. In case of sharkskin instability, pressure fluctuations inside the die indicate that its origin could also be already inside the die instead of being exclusively located at the die-exit region, as stated in earlier investigations.