CdTe thin film solar cells: device and technology issues

Polycrystalline thin film CdTe continues to be a leading material for the development of cost effective and reliable photovoltaics. Thin film CdTe solar cells and modules are typically heterojunctions with CdS being the n-type partner, or window layer. The preferred configuration for CdTe solar cells is the superstrate structure. The cadmium chloride heat treatment, the back contact formation process, and the utilization of resistive, buffer layers in tandem with a thin cadmium sulfide window layer, are important areas of research in thin film CdTe solar cells. This paper reviews work on CdTe thin film solar cells sponsored by the National Renewable Energy Laboratory. Results for a vapor chloride heat treatment with high throughput characteristics, a dry back contact process, and a comparative study of resistive buffer layers and their effect on the performance of CdTe solar cells are presented.     

Increasing the clock frequency of switched-capacitor filters

The time constant ? of a switched-capacitor (s.c.) integrator is C/(fcCR), where CR is the value of the s.c., C the integrating capacitor and fc the clock frequency. For a given ?, if fc is to increase, C/CR must increase proportionately. Since a large capacitor ratio C/CR is inconvenient to implement in an integrated circuit, most s.c. filters are clocked at the Nyquist rate. Since higher clock rates reduce switching delays, a technique of enabling higher clock frequencies without the need for large capacitor ratios has been developed.     

Effect of hexachlorocyclohexane on hsp26 expression in transgenic Drosophila melanogaster

The type and amount of lipophilic antioxidants in plasma of hyperlipidemic patients are of great importance since they play a central role in preventing deleterious oxidation of blood lipids and proteins. Isolation and quantitation of lipophilic antioxidants from hyperlipidemic plasma samples meet great obstacles because of increased levels of various intermediary lipid products. This study was designed to develop a rapid and efficient extraction and separation procedure for simultaneous analysis of ubiquinone-9 and -10 as well as alpha-, delta-, and gamma-tocopherol isomers. The levels of ubiquinone-10, alpha- and gamma-tocopherol were analyzed in human plasma samples using high-performance liquid chromatography. Lipid extraction was performed by petroleum ether/methanol/water. After phase separation, ubiquinone was reduced to ubiquinol by sodium borohydride and the lipids were separated on a C18 column. A binary gradient with solvents containing lithium perchlorate was used, and an electrochemical detector was employed for quantitation. This procedure was also efficient for the analysis of antioxidant lipids in samples containing a large number of accumulated and interfering lipid intermediates. Thus, the procedure described here is useful for efficient and rapid quantitation of ubiquinones and tocopherols in human plasma samples, especially those originating from hyperlipidemic patients.     

Controversy in spine care. Is fusion necessary after anterior cervical discectomy?

Anterior cervical discectomy is an effective and reliable treatment for nerve root or cord compression caused by disc herniation or spondylosis. Although physicians have traditionally included fusion as a part of this procedure, recent experience has suggested that this may not be necessary. Dr. Volker Sonntag and Dr. Peter Klara express opposing views on the need for fusion after discectomy and support their perspectives with clinical experience and a review of the pathoanatomy of disc disease. Dr. Sonntag believes that the majority of patients are well served with discectomy alone, avoiding the complications of graft harvest and potential nonunion. Dr. Klara feels that the interposed graft restores foraminal height and maintains cervical lordosis, both of which are important to a good outcome.     

Glycolyzed PET waste and castor oil‐based polyols for two‐pack coating systems

Useful coating products may be obtained by chemical valorization (glycolysis) of post‐consumed poly(ethylene terephthalate) (PET) wastes. Glycolysis of PET waste was carried out using poly(ethylene glycol) (PEG) of various molecular weights (200, 400, 600). The depolymerized oligoesters obtained were transesterified with castor oil which results in the formation of saturated hydroxyl‐functional polyester polyols. Two‐pack coating systems were formulated using these resins as base component and melamine formaldehyde resins as hardener component. Cured films were tested for their mechanical and chemical performances. The glycolysis of PET using PEG and polyester polyol formation was characterized using Fourier transform infrared spectroscopy and the molecular weights were determined using gel permeation chromatography. Copyright © 2006 Society of Chemical Industry     

Expression of chemokines RANTES, MIP-1alpha and GRO-alpha correlates with inflammation in acute experimental autoimmune encephalomyelitis

Experimental autoimmune encephalomyelitis (EAE) is an investigator-initiated disorder that serves as an animal model for the common human demyelinating disease multiple sclerosis. Both diseases are typified by disseminated perivascular and submeningeal cuffs in the central nervous system (CNS). It was shown recently that chemokines are integral to the pathogenesis of EAE. In the present study we analyzed the gene expression of three chemokines, RANTES, MIP-1alpha and GRO-alpha, at the onset of acute EAE, and correlated that expression with the intensity of inflammatory changes in the CNS. We showed that all three chemokines are upregulated simultaneously with symptom onset of acute EAE, and that chemokine expression correlates with the intensity of inflammation in the CNS. This consistent relationship supports the hypothesis that chemokines are relevant to leukocyte accumulation in CNS parenchyma.     

Performance analysis of optimum receivers for differentially encoded M-PSK in low SNR

A recent paper has proved that the classical receiver for coherent detection of differentially encoded M-PSK in AWGN is optimum for the MAP sequence detection criterion. In this letter, we show that asymptotically, as SNR tends to zero, the MAP symbol detection criterion receiver is equivalent to the classical differentially coherent receiver, for M greater than two. An asymptotic relative efficiency figure of merit is defined in order to compare the performances of the classical coherent receiver and the classical differentially coherent receiver.     

Inhibition of tissue repair by spironolactone: role of mineralocorticoids in fibrous tissue formation

The complete removal of the fluorescent cysteine derivative 4-(aminosulfonyl)-7-fluoro-2,1,3-benzoxadiazole (ABD-F) from an intact protein has not been demonstrated even after extended treatment with a reducing agent. It has been suggested that this may be due to incomplete denaturation under the conditions employed. We were interested in investigating this phenomenon utilizing small peptides containing individual ABD-labeled cysteine residues. After incubating the fluorescent peptides in the presence of a reductant, it was shown that the ABD label could be completely removed from all of the cysteine-containing peptides investigated. Therefore, delabeling irreversibility is due to residual structure in proteins. Electrospray ionization mass spectrometry (ESI-MS) was used to determine the molecular mass of each peptide after removal of the ABD lavel. The ESI-MS data were consistent with the generation of a free sulfhydryl. The generation of the free sulfhydryl was further substantiated when a delabeled peptide was completely relabeled with ABD-F in the absence of reductant.     

Plasma-damaged oxide reliability study correlating both hot-carrierinjection and time-dependent dielectric breakdown

The oxide damage resulting from exposure to a plasma environment in four different dry-etch tools was investigated using both hot-carrier injection (HCI) and time-dependent dielectric breakdown (TDDB). A strong correlation was observed between hot-carrier injection results and time-dependent dielectric breakdown results. It was found that a damaged oxide has both a lower critical energy for HCI to create an interface trap, and a lower activation energy for Fowler-Nordheim injection to create a hole in the oxide. These results also suggest that in dry etching, possibly more damage occurs in the metal step than in the contact etch step