bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental Investigation of Time-Frequency Characteristics of Pressure Fluctuations in a Double-Suction Centrifugal Pump
Authors: Yao Zhifeng , Wang Fujun , Qu Lixia , Xiao Ruofu , He Chenglian , Wang Min
Published: October 2011

Pressure fluctuation is the primary reason for unstable operations of double-suction centrifugal pumps. By using flush mounted pressure transducers in the semispiral suction chamber and the volute casing of a double-suction pump, the pressure fluctuation signals were obtained and recorded at various operating conditions. Spectral analyses were performed on the pressure fluctuation signals in both frequency domain and time-frequency domain based on fast Fourier transform (FFT) and an adaptive optimal-kernel time-frequency representation (AOK TFR). The results show that pressure fluctuations at the impeller rotating frequency and some lower frequencies dominated in the semispiral suction chamber. Pressure fluctuations at the blade passing frequency, the impeller rotating frequency, and their harmonic frequencies were identified in the volute casing. The amplitude of pressure fluctuation at the blade passing frequency significantly increased when the flow rate deviated from the design flow rate. At 107% of the design flow rate, the amplitude increased more than 254% than that at the design flow rate. The time-frequency characteristics of these pressure fluctuations were affected greatly by both operating conditions and measurement locations. At partial flow rates the pulsation had a great irregularity and the amplitudes at the investigated frequencies were much larger than ones at the design flow rate. An asymmetrical pressure fluctuation structure in the volute casing was observed at all flow rates. The pulsation behavior at the blade passing frequency was the most prominent near the volute tongue zone, and the pressure waves propagated in both the radial and circumferential directions.
Experimental Characterization of the Rotordynamic Forces on Space Rocket Axial Inducers
Authors: Torre Lucio , Pasini Angelo , Cervone Angelo , d’Agostino Luca
Published: October 2011

The present paper illustrates the results of an experimental campaign conducted in the Cavitating Pump Rotordynamic Test Facility (CPRTF) at ALTA S.p.A. aimed at characterizing the rotordynamic forces acting on two different whirling tapered-hub, variable-pitch axial inducers. The forces acting on the impeller have been measured by means of a rotating dynamometer mounted just behind the inducer. The roles of the imposed whirl motion of the rotor, flow coefficient, cavitation number, and liquid temperature have been investigated. The destabilizing role of cavitation has been confirmed. The experimental results are consistent with previous experimental campaigns documented by the open literature, including the former data published by Caltech researchers. The observed dependence of the tangential and normal components of the rotordynamic force on the whirl-to-rotational speed ratio does not follow the quadratic functional behavior often assumed in the open literature. Rotordynamic forces of large amplitude and destabilizing nature especially occur in the presence of cavitation, potentially compromising the stability of the pump operation.
Design of steady-state isothermal gas distribution systems consisting of long tubes in the whole range of the Knudsen number
Authors: Misdanitis Serafeim , Valougeorgis Dimitris
Published: October 2011

A novel algorithm is developed to solve steady-state isothermal vacuum gas dynamics flows through pipe networks consisting of long tubes based on linear kinetic theory. For a pipe network of known geometry the algorithm is capable of computing the mass flow rates (or the conductance) through the pipes as well as the pressure heads at the nodes of the network. The pressure distribution along each pipe element may also be found. Since a linear kinetic approach is implemented the analysis is valid and the results are accurate in the whole range of the Knudsen number, provided that the local pressure gradient along each tube of the network is small. This latter condition is satisfied when the channel is sufficiently long. The involved computational effort is very small. This is achieved by successfully integrating the linear kinetic results for the single tubes into the general solver for designing the gas pipe network. To demonstrate the feasibility of the approach two typical piping systems one in the range of small and a second one in the range of moderate Knudsen numbers are simulated. The proposed algorithm simulates, in an exact manner, low-speed gas distribution systems under any vacuum conditions based on linear kinetic modeling and constitutes a significant advancement tool in vacuum technology.
Method to compensate radiation-induced errors in a hot-cathode-ionization gauge with correcting electrode
Authors: Saeki Hiroshi , Magome Tamotsu
Published: October 2011

A previous method to compensate radiation-induced errors caused by the synchrotron radiation environment used a hot-cathode-ionization gauge with correcting electrode and shield tube. This compensating method was based on an approximate formula, and the compensated pressure measurement displayed large errors for pressures below ∼10−7 Pa. To overcome this problem, a new method, based on an exact formula, and use of precision electrometers, has now been developed and tested in a simulation experiment with excess electrons. This method reduced the pressure-measurement error to approximately 1% and is not restricted to use in a specific pressure range, even without use of a shield tube, unlike the previous method. The experimental result suggests that the new compensating method can be used in severe synchrotron radiation environments with photoelectrons.
Itk Controls the Spatiotemporal Organization of T Cell Activation
Authors: Singleton Kentner L. , Gosh Monica , Dandekar Radhika D. , Au-Yeung Byron B. , Ksionda Olga , Tybulewicz Victor L. J. , Altman Amnon , Fowell Deborah J. , Wülfing Christoph
Published: October 2011

Loss of the kinase Itk in activated T cells disrupts actin accumulation at the immunological synapse, compromising T cell activation.
Hedgehog Travels a Painful Pathway
Authors: Adler Elizabeth M.
Published: October 2011

Hedgehog signaling mediates nociceptive sensitization in flies and influences morphine analgesia in rats.
Ensuring Adequate Energy Supply
Authors: Gough Nancy R.
Published: October 2011

Mitotic kinases converge at the mitochondria to promote fission and even distribution of mitochondria in dividing cells.
Yin and Yang Stress Responses
Authors: Stern Peter R.
Published: October 2011

An imbalance between CRHR1-controlled anxiogenic glutamatergic and anxiolytic dopaminergic systems might lead to emotional disturbances.
Directing Quality Control
Authors: Hurtley Stella M.
Published: October 2011

A newly synthesized secretory protein quality control pathway is activated by direct binding of misfolded proteins to a sensor in the endoplasmic reticulum.
One Size Doesn’t Fit All
Authors: Niewold Timothy B.
Published: October 2011

Antibodies to IL-13 can treat a specific type of asthma.
Bubbles and Sound, What a Blast!
Authors: Tridandapani Srini
Published: October 2011

Bubbles plus high-intensity ultrasound can kill diseased cells and leave surrounding healthy tissue intact.
Food Animals and Antimicrobials: Impacts on Human Health
Authors: Marshall Bonnie M. , Levy Stuart B.
Published: October 2011

Antimicrobials are valuable therapeutics whose efficacy is seriously compromised by the emergence and spread of antimicrobial resistance. The provision of antibiotics to food animals encompasses a wide variety of nontherapeutic purposes that include growth promotion. The concern over resistance emergence and spread to people by nontherapeutic use of antimicrobials has led to conflicted practices and opinions. Considerable evidence supported the removal of nontherapeutic antimicrobials (NTAs) in Europe, based on the “precautionary principle.” Still, concrete scientific evidence of the favorable versus unfavorable consequences of NTAs is not clear to all stakeholders. Substantial data show elevated antibiotic resistance in bacteria associated with animals fed NTAs and their food products. This resistance spreads to other animals and humans—directly by contact and indirectly via the food chain, water, air, and manured and sludge-fertilized soils. Modern genetic techniques are making advances in deciphering the ecological impact of NTAs, but modeling efforts are thwarted by deficits in key knowledge of microbial and antibiotic loads at each stage of the transmission chain. Still, the substantial and expanding volume of evidence reporting animal-to-human spread of resistant bacteria, including that arising from use of NTAs, supports eliminating NTA use in order to reduce the growing environmental load of resistance genes.
Current Knowledge of Trichosporon spp. and Trichosporonosis
Authors: Colombo Arnaldo L. , Padovan Ana Carolina B. , Chaves Guilherme M.
Published: October 2011

Trichosporonspp. are basidiomycetous yeast-like fungi found widely in nature. Clinical isolates are generally related to superficial infections. However, this fungus has been recognized as an opportunistic agent of invasive infections, mostly in cancer patients and those exposed to invasive medical procedures. It is possible that the ability ofTrichosporonstrains to form biofilms on implanted devices, the presence of glucuronoxylomannan in their cell walls, and the ability to produce proteases and lipases are all factors likely related to the virulence of this genus and therefore may account for the progress of invasive trichosporonosis. Disseminated trichosporonosis has been increasingly reported worldwide and represents a challenge for both diagnosis and species identification. Phenotypic identification methods are useful forTrichosporonsp. screening, but only molecular methods, such as IGS region sequencing, allow the complete identification ofTrichosporonisolates at the species level. Methods for the diagnosis of invasive trichosporonosis include PCR-based methods, Luminex xMAP technology, and, more recently, proteomics. Treating patients with trichosporonosis remains a challenge because of limited data on thein vitroandin vivoactivities of antifungal drugs against clinically relevant species of the genus. Despite the mentioned limitations, the use of antifungal regimens containing triazoles appears to be the best therapeutic approach.
Trypanosoma cruzi and Chagas' Disease in the United States
Authors: Bern Caryn , Kjos Sonia , Yabsley Michael J. , Montgomery Susan P.
Published: October 2011

Chagas' disease is caused by the protozoan parasiteTrypanosoma cruziand causes potentially life-threatening disease of the heart and gastrointestinal tract. The southern half of the United States contains enzootic cycles ofT. cruzi, involving 11 recognized triatomine vector species. The greatest vector diversity and density occur in the western United States, where woodrats are the most common reservoir; other rodents, raccoons, skunks, and coyotes are also infected withT. cruzi.In the eastern United States, the prevalence ofT. cruziis highest in raccoons, opossums, armadillos, and skunks. A total of 7 autochthonous vector-borne human infections have been reported in Texas, California, Tennessee, and Louisiana; many others are thought to go unrecognized. Nevertheless, mostT. cruzi-infected individuals in the United States are immigrants from areas of endemicity in Latin America. Seven transfusion-associated and 6 organ donor-derivedT. cruziinfections have been documented in the United States and Canada. As improved control of vector- and blood-borneT. cruzitransmission decreases the burden in countries where the disease is historically endemic and imported Chagas' disease is increasingly recognized outside Latin America, the United States can play an important role in addressing the altered epidemiology of Chagas' disease in the 21st century.
1-Hexyl-2-cyanoacrylate compound (Neucrylate) bactericidal properties
Authors: Friedman Peter , Casillas Violeta , Kerber Charles W
Published: October 2011

Introduction

The need for medical grade tissue adhesives both in surgery and to treat trauma has become well established. Such a device has been developed and preliminary toxicity testing completed on a compounded cyanoacrylate (Neucrylate), and its properties have been modified so it may be used as an intravascular embolic agent. Given the high incidence of iatrogenic infections in hospital, it would be desirable to have such an implantable device that inhibits dangerous bacteria.

Materials and method

Seven separate cultures of common bacteria were grown and exposed to Neucrylate. The impact on the exposed microorganisms was analyzed visually as well as by means of fluorescence and optical microscopy.

Results

The device produced high degrees of antibacterial effect when exposed to gram positive bacteria whereas it had modest impact on gram negative bacteria.
Bovine spongiform encephalopathy associated insertion/deletion polymorphisms of the prion protein gene in the four beef cattle breeds from North China
Authors: Zhu Xiang-Yuan , Feng Fu-Ying , Xue Su-Yuan , Hou Ting , Liu Hui-Rong
Published: October 2011

Two insertion/deletion (indel) polymorphisms of the prion protein gene (PRNP), a 23-bp indel in the putative promoter region and a 12-bp indel within intron I, are associated with the susceptibility to bovine spongiform encephalopathy (BSE) in cattle. In the present study, the polymorphism frequencies of the two indels in four main beef cattle breeds (Hereford, Simmental, Black Angus, and Mongolian) from North China were studied. The results showed that the frequencies of deletion genotypes and alleles of 23- and 12-bp indels were lower, whereas the frequencies of insertion genotypes and alleles of the two indels were higher in Mongolian cattle than in the other three cattle breeds. In Mongolian cattle, the 23-bp insertion / 12-bp insertion was the major haplotype, whereas in Hereford, Simmental, and Black Angus cattle, the 23-bp deletion / 12-bp deletion was the major haplotype. These results demonstrated that Mongolian cattle could be more resistant to BSE, compared with the other three cattle breeds, because of its relatively low frequencies of deletion genotypes and alleles of 23- and 12-bp indel polymorphisms. Thus, this race could be important for selective breeding to improve resistance against BSE in this area.
A molecular genetic linkage map identifying the St and H subgenomes of Elymus (Poaceae: Triticeae) wheatgrass
Authors: Mott Ivan W. , Larson Steven R. , Jones Thomas A. , Robins Joseph G. , Jensen Kevin B. , Peel Michael D.
Published: October 2011

Elymus L. is the largest and most complex genus in the Triticeae tribe of grasses with approximately 150 polyploid perennial species occurring worldwide. We report here the first genetic linkage map for Elymus. Backcross mapping populations were created by crossing caespitose Elymus wawawaiensis (EW) (Snake River wheatgrass) and rhizomatous Elymus lanceolatus (EL) (thickspike wheatgrass) to produce F1 interspecific hybrids that were then backcrossed to the same EL male to generate progeny with segregating phenotypes. EW and EL are both allotetraploid species (n = 14) containing the St (Pseudoroegneria) and H (Hordeum) genomes. A total of 387 backcross progeny from four populations were genotyped using 399 AFLP and 116 EST-based SSR and STS markers. The resulting consensus map was 2574 cM in length apportioned among the expected number of 14 linkage groups. EST-based SSR and STS markers with homology to rice genome sequences were used to identify Elymus linkage groups homoeologous to chromosomes 1–7 of wheat. The frequency of St-derived genome markers on each linkage group was used to assign genome designations to all linkage groups, resulting in the identification of the seven St and seven H linkage groups of Elymus. This map also confirms the alloploidy and disomic chromosome pairing and segregation of Elymus and will be useful in identifying QTLs controlling perennial grass traits in this genus.
Identification and characterization of theOct4extended transcriptional regulatory region in Guanzhong dairy goat
Authors: Cheng Xiang , Meng Shuyan , Deng Jie , Lai Weifeng , Wang Huayan
Published: October 2011

The octamer-binding transcription factor 4 gene (Oct4) plays a critical role in maintaining pluripotency during early mammalian embryonic development and self-renewal of embryonic stem (ES) cells. In this study, we cloned the Oct4 cDNA and 2.8-kb regulatory region upstream of the start codon in Guanzhong dairy goat ( Capra hircus ). The comparative sequence analysis of Oct4 cDNA showed that it was highly conserved among six mammalian species. The goat Oct4 5′ regulatory regions were homologous to the corresponding regions of Oct4 in other species and were functional in directing the expression of luciferase in mouse P19 embryonic carcinoma cells and mouse J1 ES cells. Furthermore, the methylation levels in the goat Oct4 minimal promoter and proximal enhancer in the fetal genital ridge were lower than those in the heart. Additionally, two processed pseudogenes that shared high homology with goat Oct4 cDNA were identified and characterized.
Differential susceptibility of a few members of thenasuta–albomicanscomplex ofDrosophilato paraquat-induced lethality and oxidative stress
Authors: Ranjini Mysore S. , Hosamani Ravikumar , Muralidhara  , Ramachandra Nallur B.
Published: October 2011

The evolution of karyotypically stabilized short-lived (SL) and long-lived (LL) cytoraces in the laboratory have been established and validated through our previous lifespan studies. In the present investigation, we examined the possible reason(s) for the differential longevity among selected members of SL and LL cytoraces, employing the well known paraquat (PQ) resistance bioassay. Exposure of these races to varying concentrations of PQ revealed relatively higher resistance among LL cytoraces than SL cytoraces, as evident by the lower incidence of mortality. Biochemical analysis for endogenous markers of oxidative stress revealed that LL-2 cytorace exhibited lower reactive oxygen species (ROS) and lipid peroxidation (LPO) levels, higher activity levels of superoxide dismutase (SOD), and coupled with higher levels of reduced glutathione (GSH) compared with the levels found in SL-2 cytorace. These findings suggest that the higher susceptibility of SL cytoraces to PQ challenge may be, at least in part, related to the higher endogenous levels of oxidative stress markers. Although the precise mechanisms responsible for the longer longevity among LL cytoraces of the nasuta–albomicans complex of Drosophila merits further investigation, our data suggest that the relatively longer lifespan may be related to the status of endogenous markers that renders them more resistant towards oxidative-stress-mediated lethality, as evident in the PQ assay.
New species and occurrences of Bradleya Benson, 1972, Harleya Jellinek & Swanson, 2003 and Poseidonamicus Benson, 1972 (Ostracoda: Cytheroidea) from the Atlantic Sector of the Southern Ocean
Authors: Brandão Simone N. , Päplow Olinga
Published: October 2011

Abstract. The Southern Ocean shelf ostracod fauna is quite well known, while the bathyal and abyssal ones remain poorly understood. Herein, Recent Thaerocytheridae ostracods collected from deep regions in the Atlantic Sector of the Southern Ocean are described and figured. The discovery of Bradleya mesembrina Mazzini, 2005 extends its geographical and bathymetric distribution to the Antarctic zone of the Southern Ocean and to shallower (231 m) and to deeper regions (4420 m). Harleya ansoni (Whatley, Moguilevsky, Ramos & Coxill, 1998) is reported for the first time from the Weddell Sea. We also describe three new species: Poseidonamicus hunti Brandão & Päplow sp. nov., Poseidonamicus tainae Brandão sp. nov. and Poseidonamicus yasuharai Brandão & Päplow sp. nov. For the first time we provide SEM photos of the lectotype of Poseidonamicus viminea (Brady, 1880) nomen dubium. We observe that P. yasuharai displays features intermediate to Harleya and Poseidonamicus, indicating that these two genera may require new diagnoses. The bathymetric distribution of Poseidonamicus is extended to the abyssal zone and to shallower environments, and its geographical distribution is extended southwards. Finally, the inter-specific variability in the number and type of setae and claws found on several segments of Poseidonamicus limbs are intermediate between the highly variable Bairdioidea and the homogeneous Macrocyprididae.
Repeated bottom-water oxygenation during OAE 2: timing and duration of short-lived benthic foraminiferal repopulation events (Wunstorf, northern Germany)
Authors: Friedrich Oliver , Voigt Silke , Kuhnt Tanja , Koch Mirjam C.
Published: October 2011

Abstract. Published proxy data for Oceanic Anoxic Event 2 (OAE 2 or Cenomanian–Turonian Boundary Event) and other mid-Cretaceous OAEs indicate widespread anoxic bottom-water conditions. However, increasing evidence shows that anoxia was not permanent but subject to significant fluctuations. We have generated X-ray fluorescence elemental concentration and benthic foraminiferal assemblage records for a short section of OAE 2 black shales from Wunstorf, northern Germany. Two intervals of low sulphur elemental concentration are interpreted as periods of increased oxygenation of bottom waters. This is supported by benthic foraminiferal assemblage data showing repopulation events associated with these intervals. These repopulation events are characterized mainly by the occurrence of agglutinated taxa, with Lingulogavelinella globosa being the only abundant calcareous species. This observation is interpreted in terms of short-term interruptions of the otherwise anoxic bottom-water environment. Comparison with repopulation events during OAE 1b and Quaternary sapropels make it reasonable to speculate that short-term cooling and an associated increase in bottom-water ventilation at the NW European shelf sea are the main trigger mechanisms for the observed repopulation events at Wunstorf. As source area for benthic foraminifera, shallower parts of the Lower Saxony basin are proposed.
Taxonomic resolution of the Triassic–Jurassic sporomorph record in East Greenland
Authors: Mander Luke
Published: October 2011

Abstract. Sporomorphs (pollen and spores) provide valuable information about vegetation history over a range of temporal and spatial scales. However, sporomorphs can be morphologically invariant among species within genera, and among genera within certain families. In some cases, the parent plant of a sporomorph is unknown. These factors blur the relationship between sporomorph assemblages and the source vegetation, and reduce the taxonomic precision of vegetation reconstructions based on sporomorphs. This study investigates the taxonomic precision with which sporomorphs record vegetation across the Triassic–Jurassic transition (Tr–J) at Astartekløft, East Greenland. Results indicate that reconstructions of Tr–J vegetation at Astartekløft based on sporomorphs are hampered by considerable taxonomic imprecision. Something is known of the botanical affinity of almost all sporomorphs at Astartekløft at the class level, but just 50% of sporomorph taxa have a known botanical affinity at the family level. Additionally, ~23% of all sporomorph taxa at Astartekløft have affinities to more than one parent plant class, and ~36% of sporomorph taxa have affinities to more than one parent plant family. This taxonomic imprecision should be accounted for when interpreting percentage diagrams of sporomorph taxa across the Tr–J.
Calcareous nannofossil assemblage changes from early to middle Eocene in the Levant margin of the Tethys, central Israel
Authors: Weinbaum-Hefetz Menahem , Benjamini Chaim
Published: October 2011

Abstract. Patterns of change in calcareous nannofossil assemblages during nannozones NP11 to NP16 on the southern Levant margin of the Tethys were observed from sections of early and middle Eocene age sediments of the Avedat Plateau, central Israel. A cooling process following the Early Eocene Climate Optimum (EECO) is supported by several events of biotic change over a 4 Ma interval. The rate of pelagic sedimentation varied from 7.5 at the EECO to 23.6 m Ma–1 at the cooling transition phase. Reduced numbers of discoasters mark the end of the oligotrophic regime within the NP13 nannozone, followed by an increase in nannofossil richness especially marked by Blackites and Chiasmolithus spp. In the middle part of the cooling process a prominent peak of reworked Paleocene taxa, up to 7% of total taxa, suggests that enhanced current activity caused re-sedimentation on the Levant margin slopes. When stability resumed in the upper part of the NP15–16 interval, Coccolithus-type placoliths became rare and Reticulofenestra-type forms became dominant. Calcareous nannoplankton response to this gradual cooling became irreversible in the late Palaeogene, but the change was, however, diachronous across the Tethys.
Aluminum Ultra Thin Film Grown by Physical Vapor Deposition for Solar Cell Electric Nanocontacts
Authors: Karoui Abdennaceur
Published: October 2011

As aluminum film thickness and feature size fall into nanoscale, drastic and abrupt changes in optical and electric material properties occur. Reduction of Al thickness beyond a critical thickness results in island formation and local nanostructure variation. Sputter-deposited Al thin films on Si wafers were studied and the structure of grown nanofeatures is characterized. Aluminum island nanostructure has been studied for a variety of films with reference to critical thickness. Uniformly distributed Al nanoparticles with a diameter of 10 to 30 nm were formed on the silicon surface for an aimed average film thickness of 15nm. Transitions of resistivity, reflectance, and nanofeature size were observed for film thickness around 40 nm. Equally important, these properties appeared well correlated with a transformation in the film nanostructure as more Al is sputter-deposited.
A Deep-Level Transient Spectroscopy Comparison of the SiO2/Si and Al2O3/Si Interface States
Authors: Simoen Eddy , Rothschild Aude , Vermang Bart , Poortmans Jef , Mertens Robert
Published: October 2011

Deep Level Transient Spectroscopy (DLTS) has been applied to study the interface states of 5 nm Atomic Layer Deposited (ALD) Al2O3 films on p-type Si. In addition, the passivation of the interface states by Forming Gas Anneal (FGA) and Firing has been explored. It is shown that the near mid-gap density of interface states (Dit) is successfully reduced by both treatments. From a comparison with 5 nm SiO2 reference capacitors it can be concluded that similar interface defects are observed, suggesting that they are dominated by the thin interfacial SiO2 layer formed during ALD.
Effects of In Situ Boron Doping in Si Epitaxial Growth on a VIC Processed Poly-Si Seed Layer Using Hot-Wire CVD
Authors: Kang Seung Mo , Ahn Kyung Min , Lee Chang-Soo , Mun Seon Hong , Ahn Byung Tae
Published: October 2011

We investigated the epitaxial growth of large-grained poly-Si film on vapor induced crystallization (VIC) seed layer using hot-wire chemical vapor deposition(HWCVD) for hetero-junction Si solar cells. In this study, p-type poly-Si films were prepared by changing in-situ boron doping time. After epitaxial growth on VIC seed layer, average grain size of about 20μm, are obtained and the crystallographic defects in epitaxial poly-Si layer on VIC seed layer are mainly low angle grain boundaries (LAGB < 2°) and coincident site lattice boundaries (CSL), which are special boundaries of less electrical activity. Moreover, with decreasing in-situ boron doping time, mis-orientation angle and in-grain defects in epitaxial Si decrease. Using in-situ boron doping, highly doped p+ back surface field layer was fabricated, and it had high Hall mobility.
Strain Induced Nano-Structured Si1-XGeX Grown on Silicon by UHV-RTCVD for Photovoltaics
Authors: Karoui Abdennaceur , Ethiraj Anita S. , Karoui Sahtout Fouzia
Published: October 2011

Epitaxial Si1-xGex ultra-thin films deposited on the surface of silicon (001) using Ultra High Vacuum- Rapid Thermal Chemical Vapor Deposition (UHV-RTCVD) technique have been investigated using several nanoscale characterization techniques such as Atomic Force microscopy (AFM), Confocal Raman Spectroscopy, Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), and EDX. Results indicate a non-planar growth surface with the formation of various nanostructures and pits. Interfacial elastic strain energy due to lattice constant mismatch is relieved through a change in the surface morphology. This is done through the formation of 3D-islands and pits on localized strain. The islands are 3-faceted truncated pyramids with the truncated face parallel to (001). In the present work we are focusing on the characterization of the Si1-xGex/Si(001) surface morphology change during growth and thermal annealing to delineate the formation mechanisms of nano-dots at the surface of such thin film material system.
The Effect of Different Wavelengths of Light upon the Photostability of TiO2 Based Dye-Sensitized Solar Cells
Authors: Robinson Andrew J. , Holliman Peter , Connell Arthur , Worsley David
Published: October 2011

The application of Dye-Sensitized Solar Cell's (DSC's) to metal substrates is a potentially exciting leap in the application of DSC technology to building integrated photovoltaics (BIPV). Currently, the most cost efficient DSCs use TiO2 as a working electrode. A significant challenge for extending device lifetime is the effective shielding of the TiO2 to light of wavelengths lower than 387nm (band gap of anatase TiO2) and 413nm (band gap of rutile TiO2). This paper presents a convenient method to measure in situ TiO2 photoactivity by measuring the gaseous by-products (CO2, H2O and HCl) of photo-catalytic mineralisation of homogeneous PVC-TiO2 films. Measurements have been made using a specially developed UV irradiation cell attached to a closed loop FTIR CO2 Detection Reactor. This experimental set up has been used in combination with Schott glass filters to evaluate the kinetics of photo-degradation by monitoring CO2 evolution at various different wavelengths of light.
Electrochemical Characterization of the UV-Photodegradation of Dye-Sensitized Solar Cells and Usage in the Assessment of UV-Protection Measures
Authors: Carnie Matthew J. , Watson Trystan , Bryant D. T. , Worsley David
Published: October 2011

Within just 400 light hours exposure of UVA irradiation (λ max 365 nm), glass mounted dye-sensitized solar cells with no UV filtration begin to fail drastically. The failure mode is shown to relate to electrolyte degradation rather than dye photo-bleaching and that this is directly related to TiO2 photo-catalysis. The onset of failure is determined in less than 120 hours using electrochemical impedance data where the resistance of the electronic back reaction, between the TiO2 semi-conductor and the electrolyte, drops markedly prior to the onset of degradation. At the point of complete cell failure this impedance value then dramatically increases as there is no longer an interfacial reaction possible between the TiO2 and the degraded electrolyte. The degradation is most rapid for cells under electrical load indicating that the degradation of the electrolyte is related to hole production by direct excitation of the TiO2.
Branched TiO2 Nanorods Covered with TiO2 Nanosheets for Harvesting Solar Energies in Dye-Sensitized Solar Cells
Authors: Guo Wenxi , Zheng Dajiang , Lu Miaoqiang , Lin Chang-Jian , Wang Zhong Lin
Published: October 2011

A hierarchical structure of branched TiO2 nanorods covered with TiO2 nanosheets was designed and constructed for harvesting solar energies in dye-sensitized solar cells. Vertical aligned TiO2 nanorod arrays were synthesized on fluorine-doped SnO2 (FTO) by using the electrochemically deposited ZnO nanorod arrays as a template and liquid phase deposition (LPD) method. The resultant TiO2 nanorod was used as a seed and the rutile TiO2 nanorods were firstly synthesized on the surface of anatase TiO2 nanorod by using hydrothermal method. In photocurrent-voltage measurements, 3.56% efficiency was achieved for 1.5um thick nanosheets coated TiO2 nanobranch (NB), which is about 239% higher than the original TiO2 nanorod arrays.
ZnO Nanowire Arrays Sensitized with Different Absorber Materials for Fabrication of Nanostructured Solar Cells
Authors: Salazar Raul , Sanchez Sylvia , Delamoreanu Alexandru , Lévy-Clément Claude , Ivanova Valentina
Published: October 2011

In this manuscript we report the photosensitization of electrodeposited ZnO nanowire arrays with CdS, CdTe, CuZnS (CZS) and Cu2ZnSnS4 (CZTS) extremely thin films prepared by: Successive Ion Layer Absorption and Reaction (SILAR), electrochemical deposition (ECD) and Close Space Sublimation (CSS) methods. The structural and optical properties of the ZnO/absorber nanostructures were characterized. 25 nm thick CdS nanoparticle-like shell was obtained after 40 deposition cycles by SILAR. CdTe shell deposited by the same technique is about 15 nm thick (for 20 cycles), whereas the CZS shell is thicker (40 nm) after 3 cycles. The layer thickness is controlled by the deposition cycles number. The CdTe film deposited by CSS (about 40 nm thick) is formed by 20 nm large nanoparticles. The thickness of electrodeposited CZTS layer is controlled by the passed deposition charge density. The room-temperature wet processes appear suitable to prepare good quality and uniform nanometer-thick films of absorbing materials.
Antimony Sulfide Absorbers in Solar Cells
Authors: Nair P. K. , González-Lua Rogelio , Calixto Rodríguez Manuela , Capistrán Martínez Jesús , GomezDaza Oscar , Nair M. T. Santhamma
Published: October 2011

Abundance of antimony in the earth's upper crust is near 0.2 ppm, with an annual production nearly two hundred thousand tons, and 99.65% ingot price below US$15/kg, thus making antimony-based semiconductor compounds attractive for solar cells. The optical band gap (Eg) 1.5-1.8 eV of antimony sulfide qualifies it as a solar cell absorber, particularly in view of the solid solutions Sb2Se3-xSe with Eg 1-1.8 eV. We report here chemical deposition Sb2S3 of 300 nm in thickness using two methods. When used in CdS/Sb2S3/C-Ag cells prepared by either method, Voc is up to 640 mV and Jsc, 2-5 mA/cm2 and efficiency, η is 0.5-1% under 1000 W/m2 AM 1.5 G sunlight. Under concentrated sunlight, Jsc increases proportionately and Voc, logarithmically. Addition of a 400 nm of PbS thin film: CdS/Sb2S3/PbS/C-Ag improves Voc, but cell efficiency is 1%.
Chemically Deposited Tin Chalcogenides as Absorbers in Thin Film Solar Cells
Authors: Nair M. T. Santhamma , Barrios-Salgado Enue , García Ana Rosa , Aragón-Silva Maricela Rebeca , Campos José , Nair P. K.
Published: October 2011

Attractive optical and electrical properties of tin chalcogenides, along with the abundance of Sn in the earth's crust project themselves as alternate p-type absorber materials in thin-film photovoltaic technologies. Cell structures prepared with SnS (ZB) of 500 nm and colloidal graphite paint as back contact showed a Voc of 344 mV, Jsc of 3.1 mA/cm2 with a fill factor FF of 0.37 and conversion efficiency η of 0.57 %. In SnO2:F/CdS/Sb2S3/SnSe cells prepared with an evaporated SnSe film, Voc of 607 mV, Jsc 3.9 mA/cm2 FF 0.26 and η of 0.61 % is obtained. We present here the details of the cell preparation and their characteristics.
Hybrid Nitride-ZnO Solar Cells
Authors: Namkoong Gon , Diefeng Gu , Foe Kurniawan , Bae S.Y. , Kim D.H. , Seo D.J. , Lee D.S. , Jeon S.R. , Baumgart Helmut
Published: October 2011

We investigated the effect of polarization of III-nitrides upon the energy band structures and the circuit voltage (VOC) in nitride solar cells. We found that the strong spontaneous polarization will adversely reduce the open circuit voltage (VOC) in p-i-n nitride solar cells. On the contrary, the piezoelectric polarization in InGaN/GaN MQW solar cells does not play a significant role in reducing the open circuit voltage. As an alternative to p-i-n nitride solar cells, based on theoretical energy band structures we propose hybrid InGaN/ZnO solar cells which do not have an adverse influence on the reduction of the VOC. We fabricated hybrid p-GaN/n-ZnO solar cells and demonstrated for the first time the photovoltaic effects.
A Greener Electrodeposition Recipe for ZnO Films
Authors: Zhou Bin , Feng Qing , Tao Meng
Published: October 2011

Electrodeposition of ZnO films can be performed in an aqueous solution using a greener recipe, where the solution can be reused for multiple deposition runs. The solution in this greener recipe contains KCl to provide electrical conductivity to allow the deposition reactions. A Zn foil serves as the Zn source, which dissolves during the deposition. O2 is bubbled into the solution as the oxygen source. This recipe eliminates concentration change in the solution as deposition proceeds, making the solution reusable. Multiple deposition runs for ZnO films in the same solution have been demonstrated. X-ray diffraction, optical transmittance and absorption spectra reveal that all the obtained ZnO films have similar structural and optical properties. They display high transmittance of ~80% and low absorbance of ~10%. Moreover, an initial Zn2+ concentration in the solution is required, not to serve as a Zn source but to facilitate the deposition.
Effects of Na Precursor Layer Deposited on Mo Substrate about (In,Ga)2Se3 and CIGS Layers
Authors: Shin Young Min , Lee Chang-Soo , Ahn Byung Tae
Published: October 2011

Na external doping using Na2S precursors on Mo/Corning glass substrate is one of the simplest doping methods. But the method affects both surface morphology and preferred orientation of (In,Ga)2Se3 and CIGS films, especially when the thickness was increased. The textures of CIGS films prepared with 3-stage process appear to be inherited from the textures of the (In,Ga)2Se3 films deposited during the first stage, it can be assumed that the growth of (In,Ga)2Se3 films were modified with Na2S precursors. As the thickness of Na precursor was increased, surface morphology of (In,Ga)2Se3 films was more smooth than that of the films which had thin Na precursor. And CIGS thin films made by these (In,Ga)2Se3 films showed that (112) orientation was stronger than (220/204) orientation. And also it was investigated there is a close relation about the morphology and the roughness between (In,Ga)2Se3 and CIGS films by AFM.
Fabrication of Zn1-xMgxO Buffer Layers for CIGS Solar Cells by Atomic Layer Deposition Using Mg(CpEt)2 as a Mg Source
Authors: Lee Chang-Soo , Shin Young Min , Ahn Byung Tae
Published: October 2011

Zn1-xMgxO thin films with wurzite structure were deposited by the ALD process using diethylzinc (Zn(C2H5)2) and bis-ethyl-cyclopentadienyl-magnesium (Mg(CpEt)2) as metal precursors and water vapor as a reactant. We confirmed that the bandgap energy of the Zn1-xMgxO films increase as Mg contents increases, and bandgap energy and chemical composition can be precisely controlled by MgO/ZnO cycle ratio. The CIGS solar cells using Zn1-xMgxO buffer layer showed 12.5% energy conversion efficiency. Based on these properties, we suggest that Zn1-xMgxO thin films deposited by ALD using Mg(CpEt)2 can be used as the buffer layer for Cu(In,Ga)Se2 solar cells.
CuInS2 Quantum Dots Coated with CdS as High-Performance Sensitizers for TiO2 Electrodes in Hydrogen Production and Photovoltaic Applications
Authors: Li Tzung-Luen , Teng Hsisheng
Published: October 2011

We demonstrate a high-performance photoanode composed of a nanoporous TiO2 film co-sensitized with CuInS2 quantum dots (QDs) and CdS polycrystalline layers, exhibiting the excellent performance in both photosynthetic and photovoltaic applications. The CuInS2 QDs are synthesized via a solvothermal route and the average particle size is 3.5 nm, attached on TiO2 surface by assistance of bifunctional linker. The subsequent CdS layers are coated using successive ionic layer adsorption and reaction. The back reaction of interfacial charge recombination can be prohibited by the CdS coating. Besides, the CdS shell coating results in remission of the quantum confinement of the QDs, leading to a widening of optical absorption spectra. In a photosynthetic photoelectrochemical cell, this heterostructural electrode exhibits a saturated photocurrent of 16 mA cm-2 under illumination of AM 1.5G at full sun intensity. On the other hand, this high-performance photoanode exhibits a power conversion efficiency of 4.08% in a sandwich-type quantum dot sensitized solar cells (QDSSCs) using CuS as counter electrode. The superior performance is mainly ascribed to the extension of the absorption spectra and significant enhancement of charge separation via CdS coating.
Fabrication of Cu(In,Ga)Se2 Thin Film by Selenization of Stacked Elemental Layer with Solid Selenium
Authors: Li Zhao-Hui , Cho Eou-Sik , Kwon Sang Jik , Dagenais Mario
Published: October 2011

Cu(In,Ga)Se2 thin films were prepared using the classical two-step process approach. In the first step, the metallic precursors were deposited on the soda-lime glass substrates by electron-beam evaporation following the Cu/In/Ga... sequence. The selenization, called the second step, was produced in a rapid thermal processor. This process performed under nitrogen atmosphere of 200 Torr at 200°C for 5 minutes followed by 500°C for 3 minutes. The device quality of CIGS film, with the atomic ratios of Cu/(In+Ga) of 0.90 and Ga/(In+Ga) of 0.26, was obtained when the Cu/In/Ga metallic layer had thinness ratio of 900 Aå/600 Aå /200 Aå. The CIGS film with homogeneous and dense surface morphology with large grain size (~ 2 μm) was formed.
The Thermal Response of Gallium Nitride HFET Devices Grown on Silicon and SiC Substrates
Authors: Donmezer Fatma N. , James William , Graham Samuel
Published: October 2011

In this study a multi-scale thermal approach is presented and used for the prediction of the hotspot temperature of AlGaN/GaN Heterojunction Field Effect Transistors(HFETs) grown on Si and SiC substrates. The multi-scale approach accounts for heat generation within the device obtained using Sentaurus Device Simulator. The heat generation regions within the device were found to be highly localized to nanometer sized domains. Heat transfer modeling in the small heat generation region was performed by solving the gray phonon BTE to capture the ballistic-diffusive nature of phonon transport. This model was coupled to a diffusive thermal transport finite element code (COMSOL) to extend the device domain and obtain the thermal boundary conditions for the smaller BTE domain. The calculated hotspot temperatures under different biasing conditions were compared for devices grown on Si/SiC substrates. The impact of the heat dissipation path and methods to reduce hot spot temperature are discussed.
Space Charge Limited Current and Polarization in AlGaN/GaN Nanowires
Authors: Mastro Michael , Kim H.-Y. , Ahn J. , Kim J. , Hite J.K. , Eddy C.R.
Published: October 2011

An undoped AlGaN/GaN nanowire displayed a transition at approximately 2V from Ohmic conduction at low drain-source voltage to space charge limited conduction at high drain-source voltage. Growth of the nanowire from a metal seed manifests as a triangular cross-section with one Ga-polar (0001) facet and two semi-polar {-110-1} facets. Conduction was based on a polarization induced two-dimensional electron gas that formed at the (0001) AlGaN/GaN interface. A simulation showed that the surface and the opposing polarization field at the semi-polar AlGaN/GaN interface will distort and reduce the carrier concentration at the (0001) AlGaN/GaN interface.
Effect of the Source Field Plate on AlGaN/GaN High Electron Mobility Transistors during Off-State Stress
Authors: Liu Lu , Kang Tsung-Sheng , Cullen David A. , Zhou Lin , Kim Jinhyung , Chang C. Y. , Douglas Erica , Jang Soohwan , Smith David J. , Pearton S. J. , Johnson Wayne J. , Ren F.
Published: October 2011

The effects of source field plates on AlGaN/GaN High Electron Mobility Transistor reliability under off-state stress conditions were investigated using step-stress cycling. The source field plate enhanced the drain breakdown voltage from 55V to 155V and the critical voltage for off-state gate stress from 40V to 65V, relative to devices without the field plate. Transmission electron microscopy (TEM) was used to examine the degradation of the gate contacts and revealed the presence of cracking due to the inverse piezoelectric effect that appeared on both source and drain side of the gate edges. A thin oxide layer was observed between the Ni gate contact and the Semiconductor, and both Ni and oxygen diffused into the AlGaN layer after stress.
Reliability Issues in AlGaN/GaN High Electron Mobility Transistors
Authors: Douglas Erica , Liu Lu , Lo Chien-Fong , Gila Brent P. , Ren F. , Pearton S. J.
Published: October 2011

As AlGaN/GaN high electron mobility transistors gain commercial acceptance for use in high power and high frequency applications, it is becoming ever important to understand the degradation mechanisms that drive failure in the field. Because of the complex nature and multi-faceted operation modes of these devices, reliability studies must go beyond the typical Arrhenius accelerated life tests. To do this, we investigated the electric field driven degradation in devices with different gate metallization, device dimensions, electric field mitigation techniques (such as source field plate), and the effect of device fabrication processes for both dc and RF stress conditions.
Lattice-Matched and Strain-Compensated Materials for Mid-Wave and Long-Wave Infrared Quantum Cascade Lasers
Authors: Wang Christine A. , Calawa Daniel R. , Goyal Anish , Menzel Stefan , Capasso Federico
Published: October 2011

This work reports the growth and characterization of lattice-matched (LM) and strain-compensated (SC) AlInAs/GaInAs/InP heterostructures for quantum cascade lasers (QCLs) emitting in the mid-wave infrared (MWIR) and long-wave infrared (LWIR) wavelength regions. Organometallic vapor phase epitaxy growth conditions such as temperature, growth rate, and V/III ratio were varied to establish a step-flow growth mode. Multiple-quantum-well structures with either (LM) or with SC compressive GaInAs quantum wells and tensile AlInAs barriers were grown to optimize QCL structure growth. Atomic force microscopy and high-resolution x-ray diffraction data indicate excellent structural quality materials for QCLs. LM LWIR QCLs at 9.6 μm have pulsed peak power as high as 2.5 W/facet and pulsed wall-plug efficiency of 5.4%, while SC MWIR QCLs at 4.8 µm have peak power of 1.7 W and 9.7% pulsed wall-plug efficiency. SC MWIR QCLs exhibit very low threshold current density of 0.8 kA/cm2.
Investigation of Electrodeposited and Solution Grown ZnO Nanorod Based UV Photodetector
Authors: Dalui Saikat
Published: October 2011

In this work solution growth technique as well as electrodepostion technique was employed to directly grow ZnO nanorod arrays on the p-GaN layer for fabricating n-ZnO nanorod/ p-GaN heterojunction diodes. Microstructure and room temperature photoluminescence (PL) measurement confirmed the growth of ZnO nanorod arrays with near perfect microstructure, stoichiometry and excellent optical quality. Current-voltage (I-V) measurements showed the formation of diode structure with a typical diode characteristic having a turn on voltage of 2.5V and 6.4V respectively, for solution grown and electrodeposited ZnO nanorod based p-n diode. A low resistive ITO coated glass was used to make contact with the top nanorod arrays and spectral response of the p-n diode was investigated. UV response particularly from solution grown ZnO nanorod based p-n diode was very promising.