bluuebunny/crossref_metadata_2025 huggingface dataset:
Inactivation of the Transcriptional Regulator-Encoding Gene
sdiA
Enhances Rice Root Colonization and Biofilm Formation in Enterobacter cloacae GS1
Authors: Shankar Manoharan , Ponraj Paramasivan , Illakkiam Devaraj , Rajendhran Jeyaprakash , Gunasekaran Paramasamy
Published: October 2012

Enterobacter cloacae
GS1 is a plant growth-promoting bacterium which colonizes rice roots. In the rhizosphere environment,
N
-acyl homoserine lactone (NAHL)-like quorum-sensing signals are known to be produced by host plants and other microbial inhabitants.
E. cloacae
GS1 was unable to synthesize NAHL quorum-sensing signals but had the NAHL-dependent transcriptional regulator-encoding gene
sdiA
. This study was aimed at understanding the effects of SdiA and NAHL-dependent cross talk in rice root colonization by
E. cloacae
GS1. Pleiotropic effects of
sdiA
inactivation included substantial increases in root colonization and biofilm formation, suggesting a negative role for SdiA in bacterial adhesion. We provide evidence that
sdiA
inactivation leads to elevated levels of biosynthesis of curli, which is involved in cellular adhesion. Extraneous addition of NAHLs had a negative effect on root colonization and biofilm formation. However, the
sdiA
mutant of
E. cloacae
GS1 was insensitive to NAHLs, suggesting that this NAHL-induced inhibition of root colonization and biofilm formation is SdiA dependent. Therefore, it is proposed that NAHLs produced by both plant and microbes in the rice rhizosphere act as cross-kingdom and interspecies signals to negatively impact cellular adhesion and, thereby, root colonization in
E. cloacae
GS1.
The Sakaguchi Reaction Product Quenches Phycobilisome Fluorescence, Allowing Determination of the Arginine Concentration in Cells of Anabaena Strain PCC 7120
Authors: Ke Shan , Haselkorn Robert
Published: October 2012

The filamentous cyanobacterium
Anabaena
fixes nitrogen in specialized cells called heterocysts. The immediate product of fixation, ammonia, is known to be assimilated by addition to glutamate to make glutamine. How fixed nitrogen is transported along the filament to the 10 to 20 vegetative cells that separate heterocysts is unknown. N-fixing heterocysts accumulate an insoluble polymer containing aspartate and arginine at the cell poles. Lockau's group has proposed that the polymer is degraded at the poles to provide a mobile carrier, arginine, to the vegetative cells (R. Richter, M. Hejazi, R. Kraft, K. Ziegler, and W. Lockau, Eur. J. Biochem.
263:
163–169, 1999). We wished to use the Sakaguchi reaction for arginine to determine the relative cellular concentration of arginine along the filament. At present, the methods for measuring absorption of the Sakaguchi reaction product at 520 nm are insufficiently sensitive for that purpose. However, that product quenches the fluorescence of phycobiliproteins, which we have adapted to a determination of arginine. Our results are consistent with the proposal that arginine is a principal nitrogen carrier from heterocysts to vegetative cells in
Anabaena
.
Identification and Characterization of a Highly Conserved Crenarchaeal Protein Lysine Methyltransferase with Broad Substrate Specificity
Authors: Chu Yindi , Zhang Zhenfeng , Wang Qian , Luo Yuanming , Huang Li
Published: October 2012

Protein lysine methylation occurs extensively in theCrenarchaeota, a major kingdom in theArchaea. However, the enzymes responsible for this type of posttranslational modification have not been found. Here we report the identification and characterization of the first crenarchaeal protein lysine methyltransferase, designated aKMT, from the hyperthermophilic crenarchaeonSulfolobus islandicus. The enzyme was capable of transferring methyl groups to selected lysine residues in a substrate protein usingS-adenosyl-l-methionine (SAM) as the methyl donor. aKMT, a non-SET domain protein, is highly conserved among crenarchaea, and distantly related homologs also exist inBacteriaandEukarya. aKMT was active over a wide range of temperatures, from ∼25 to 90°C, with an optimal temperature at ∼60 to 70°C. Amino acid residues Y9 and T12 at the N terminus appear to be the key residues in the putative active site of aKMT, as indicated by sequence conservation and site-directed mutagenesis. Although aKMT was identified based on its methylating activity on Cren7, the crenarchaeal chromatin protein, it exhibited broad substrate specificity and was capable of methylating a number of recombinantSulfolobusproteins overproduced inEscherichia coli. The finding of aKMT will help elucidate mechanisms underlining extensive protein lysine methylation and the functional significance of posttranslational protein methylation in crenarchaea.
AglS, a Novel Component of the Haloferax volcanii N-Glycosylation Pathway, Is a Dolichol Phosphate-Mannose Mannosyltransferase
Authors: Cohen-Rosenzweig Chen , Yurist-Doutsch Sophie , Eichler Jerry
Published: October 2012

In
Haloferax volcanii
, a series of Agl proteins mediates protein N-glycosylation. The genes encoding all but one of the Agl proteins are sequestered into a single gene island. The same region of the genome includes sequences also suspected but not yet verified as serving N-glycosylation roles, such as
HVO
_
1526
. In the following, HVO_1526, renamed AglS, is shown to be necessary for the addition of the final mannose subunit of the pentasaccharide N-linked to the surface (S)-layer glycoprotein, a convenient reporter of N-glycosylation in
Hfx. volcanii
. Relying on bioinformatics, topological analysis, gene deletion, mass spectrometry, and biochemical assays, AglS was shown to act as a dolichol phosphate-mannose mannosyltransferase, mediating the transfer of mannose from dolichol phosphate to the tetrasaccharide corresponding to the first four subunits of the pentasaccharide N-linked to the S-layer glycoprotein.
Transcription Factor Family-Based Reconstruction of Singleton Regulons and Study of the Crp/Fnr, ArsR, and GntR Families in Desulfovibrionales Genomes
Authors: Kazakov Alexey E. , Rodionov Dmitry A. , Price Morgan N. , Arkin Adam P. , Dubchak Inna , Novichkov Pavel S.
Published: October 2012

Accurate detection of transcriptional regulatory elements is essential for high-quality genome annotation, metabolic reconstruction, and modeling of regulatory networks. We developed a computational approach for reconstruction of regulons operated by transcription factors (TFs) from large protein families and applied this novel approach to three TF families in 10
Desulfovibrionales
genomes. Phylogenetic analyses of 125 regulators from the ArsR, Crp/Fnr, and GntR families revealed that 65% of these regulators (termed reference TFs) are well conserved in
Desulfovibrionales
, while the remaining 35% of regulators (termed singleton TFs) are species specific and show a mosaic distribution. For regulon reconstruction in the group of singleton TFs, the standard orthology-based approach was inefficient, and thus, we developed a novel approach based on the simultaneous study of all homologous TFs from the same family in a group of genomes. As a result, we identified binding for 21 singleton TFs and for all reference TFs in all three analyzed families. Within each TF family we observed structural similarities between DNA-binding motifs of different reference and singleton TFs. The collection of reconstructed regulons is available at the RegPrecise database (
http://regprecise.lbl.gov/RegPrecise/Desulfovibrionales.jsp
).
HIV among people who inject drugs in Central and Eastern Europe and Central Asia: a systematic review with implications for policy
Authors: Jolley Emma , Rhodes Tim , Platt Lucy , Hope Vivian , Latypov Alisher , Donoghoe Martin , Wilson David
Published: October 2012

Background and objectives

HIV among people who inject drugs (PWID) is a major public health concern in Eastern and Central Europe and Central Asia. HIV transmission in this group is growing and over 27 000 HIV cases were diagnosed among PWID in 2010 alone. The objective of this systematic review was to examine risk factors associated with HIV prevalence among PWID in Central and Eastern Europe and Central Asia and to describe the response to HIV in this population and the policy environments in which they live.

Design

A systematic review of peer-reviewed and grey literature addressing HIV prevalence and risk factors for HIV prevalence among PWID and a synthesis of key resources describing the response to HIV in this population. We used a comprehensive search strategy across multiple electronic databases to collect original research papers addressing HIV prevalence and risk factors among PWID since 2005. We summarised the extent of key harm reduction interventions, and using a simple index of ‘enabling’ environment described the policy environments in which they are implemented.

Studies reviewed

Of the 5644 research papers identified from electronic databases and 40 documents collected from our grey literature search, 70 documents provided unique estimates of HIV and 14 provided multivariate risk factors for HIV among PWID.

Results

HIV prevalence varies widely, with generally low or medium (<5%) prevalence in Central Europe and high (>10%) prevalence in Eastern Europe. We found evidence for a number of structural factors associated with HIV including gender, socio-economic position and contact with law enforcement agencies.

Conclusions

The HIV epidemic among PWID in the region is varied, with the greatest burden generally in Eastern Europe. Data suggest that the current response to HIV among PWID is insufficient, and hindered by multiple environmental barriers including restricted access to services and unsupportive policy or social environments.
Rheumatic heart disease: pilot study for a population-based evaluation of prevalence and cardiovascular outcomes among schoolchildren in Nepal
Authors: Shrestha Nikesh Raj , Kalesan Bindu , Karki Prahlad , Sherpa Kunjang , Basnet Anil , Urban Philip , Pilgrim Thomas
Published: October 2012

Objectives

To evaluate a protocol for a population-based programme targeting the prevention of rheumatic heart disease (RHD) progression by early echocardiographic diagnosis of valvular lesions and timely implementation of secondary prevention.

Design

Observational survey with a subsequent prospective cohort study.

Setting

Private boarding school in the urban area of the Sunsari district situated on the foothills of the Lower Himalayan Range in Eastern Nepal.

Participants

Fifty-four unselected school-going children 5–15 years of age, 24 girls and 30 boys.

Primary outcome measure

Logistic feasibility of a large-scale population-based screening study using the echocardiographic criteria formulated by the World Heart Federation, with longitudinal follow-up of children with definite or borderline RHD in a prospective cohort study.

Results

Standardised interview, physical examination and screening echocardiography were performed in a three-staged process and took approximately 6 min per child. Socio-economic status was assessed using surrogate markers such as the occupation of the primary caregiver, numbers of rooms at home, car, television, cell phone and internet connection. Physical examination was focused on cardiac auscultation and signs of acute rheumatic fever and targeted echocardiography was performed by an independent examiner without knowledge of the clinical findings. Two children with evidence of borderline RHD were re-examined at B.P. Koirala Institute of Health Sciences and the indication for secondary antibiotic prevention was discussed with the parents and the children. At 6 months of follow-up, echocardiographic findings were stable in both children. Implementation of secondary antibiotic prevention was challenged by impaired awareness of subclinical RHD among parents and inadequate cooperation with family physicians.

Conclusions

This pilot study shows that the methods outlined in the protocol can be translated into a large-scale population-based study. We learned that education and collaboration with teachers, parents and family physicians/paediatricians will be of key importance in order to establish a sustainable programme.
Screening for HIV among tuberculosis patients: a cross-sectional study in Sindh, Pakistan
Authors: Hasnain Jamshed , Memon Ghulam Nabi , Memon Ashraf , Channa Abid Ali , Creswell Jacob , Shah Sharaf Ali
Published: October 2012

Objective

To describe feasibility and results of systematic screening of tuberculosis (TB) patients for HIV.

Design

Cross-sectional study.

Setting

Six selected sentinel sites (public DOTS clinics) in the province of Sindh, Pakistan.

Participants

All TB patients aged 16–60 years registered for treatment from April 2008 to March 2012.

Measurement

Demographic information of registered TB patients, screening for HIV through rapid testing and confirmation by referral lab of Sindh AIDS Control Program, according to national guidelines.

Results

Of a total of 18 461 registered TB patients, 12 882 fulfilled the inclusion criteria and were given education and counselling. Of those counselled 12 552 (97.4%) were screened for HIV using a rapid test. Men made up 48% of the sample and 76.5% of patients had pulmonary TB. Of the total patients tested, 42 (0.34%) were HIV-positive after confirmatory testing at the Sindh AIDS Control Program Laboratory. Prevalence of HIV among male patients was 0.67% whereas prevalence among female patients was 0.03% (p value <0.001). Prevalence of HIV among pulmonary TB patients was 0.29% and among extrapulmonary TB patients was 0.48% (p value=0.09).

Conclusion

In public DOTS clinics in Pakistan it is feasible to test TB patients for HIV. Prevalence of HIV is three times higher among TB patients as compared with the general population in Pakistan. Although the results are not representative of Pakistan or Sindh province they cover a large catchment area and closely match WHO estimate for the country. Routinely screening all TB patients for HIV infection, especially targeting men and ensuring antiretroviral therapy, can significantly improve TB/HIV collaborative activities in Pakistan and identify many cases of HIV, improve health outcomes and save lives.
Her2 amplification distinguishes a subset of non-muscle-invasive bladder cancers with a high risk of progression
Authors: Chen Paul Chih-Hsueh , Yu Hui-Jung , Chang Yen-Hwa , Pan Chin-Chen
Published: October 2012

Background

Several studies have employed immunohistochemistry to detect Her2/neuoverexpression in urothelial carcinomas, yielding a tremendous range of positive expression rates. Few studies have examined Her2 status in non-muscle invasive bladder cancer (NMIBC) using fluorescence in situ hybridisation (FISH).

Aim

To evaluate Her2 amplification in NMIBC (Ta/T1), to correlate the findings with recurrence and progression, and compare the Her2 status between primary and progressive tumours.

Methods

FISH and immunohistochemistry for Her2/neuwere performed on tissue arrays consisting of 36 papillary urothelial neoplasms of low malignant potential (PUNLMPs), 190 low grade urothelial carcinomas (LG-UCs) and 178 high grade urothelial carcinomas (HG-UCs). 32 cases with specimens of both primary and progressive tumours (from Ta/T1 to T2–4) were included for comparative analyses.

Results

16 HG-UCs (9.0%) showed Her2 gene amplification while none of the PUNLMPs and LG-UCs showed this aberration. There was 100% concordance in the status of Her2 amplification between primary and progressive lesions. Immunohistochemistry and FISH results were in closest agreement when overexpression was defined as 50% of tumour cells showing immunoreactivity. The cumulative incidences of recurrence and progression in Her2-amplified HG-UC were significantly higher than in those without amplification.

Conclusions

A subset of high-grade NMIBCs contain Her2 amplification and are associated with markedly aggressive behaviour. Her2 diagnostics are valuable for distinguishing patients who require diligent surveillance and would potentially benefit from anti-Her2 therapies.
CD24: a potential new marker in differentiating malignant mesothelioma from pulmonary adenocarcinoma
Authors: Pinato David J , Nya Paul , Sharma Rohini , Mauri Francesco A
Published: October 2012

Background

The differential diagnosis between malignant mesothelioma (MM) and metastatic lung adenocarcinoma (MLA) often relies on immunohistochemical studies, with no individual immunomarker holding satisfactory discrimination ability.

Methods

We investigated the diagnostic accuracy of CD24 immunoreactivity on 134 patients including 69 cases of MM and 65 MLA.

Results

The expression of CD24 favoured MLA, with 57/65 cases showing positive cytoplasmic staining compared with 9/69 MM (p<0.001), whose immunopositivity pattern was prevalently membranous (7/9 cases).

Conclusions

CD24 positivity can accurately discriminate MM from MLA. Prospective studies are warranted to clarify whether CD24 could integrate with other immunomarkers to facilitate the diagnosis of mesothelial malignancies.
Better retrieval of lymph nodes in colorectal resection specimens by pathologists’ assistants
Authors: Kuijpers C C H J , van Slooten H J , Schreurs W H , Moormann G R H M , Abtahi M A , Slappendel A , Cliteur V , van Diest P J , Jiwa N M
Published: October 2012

Background

Errors in surgical pathology are partly due to the increasing workload of pathologists. To reduce this workload, ‘pathologists’ assistants’ (PAs) have been trained to take over some of the pathologists’ recurrent tasks. One of these tasks is the precise examination of ≥10 lymph nodes (LNs), which is of paramount importance to reduce the risk of understaging of colorectal cancer patients.

Aims

To evaluate the role of PAs in harvesting LNs in colorectal resection specimens and, by doing so, in improving patient safety.

Methods

LN harvest was retrospectively reviewed in 557 pathology reports on colorectal resection specimens collected in two Dutch hospitals from 2008 until 2011.

Results

PAs sampled ≥10 LNs in significantly more cases than pathologists did (83.2% vs 60.9% in hospital A and 79.2% vs 67.6% in hospital B) and recovered on average significantly more LNs than pathologists did (18.5 vs 12.2 in hospital A and 16.6 vs 13.2 in hospital B). PAs harvested a significantly higher percentage of LNs <5 mm than pathologists did (64.2% vs 53.7%). The percentages of colon cancer patients eligible for adjuvant chemotherapy due to inadequate LN sampling alone were significantly higher for cases dissected by pathologists than for those dissected by PAs (17.3% vs 1.1% in hospital A and 13.1% vs 3.4% in hospital B)

Conclusions

PAs contribute to patient safety since they recover more and, in particular, smaller LNs from colorectal resection specimens than pathologists do. Moreover, they help to reduce costs and morbidity by reducing the number of patients eligible for adjuvant chemotherapy due to inadequate LN sampling alone.
The manufacture and assessment of tissue microarrays: suggestions and criteria for analysis, with breast cancer as an example
Authors: Pinder Sarah E , Brown John P , Gillett Cheryl , Purdie Colin A , Speirs Valerie , Thompson Alastair M , Shaaban Abeer M
Published: October 2012

Tissue microarray (TMA) is an established and valuable tool, particularly in translational research and clinical trials, allowing resource-efficient use, and high-throughput profiling, of large numbers of tumours. Despite this, there is little evidence, or guidance, on the optimum manufacture, use and assessment of TMAs. Here we review some of the literature, using breast cancer as an example, to highlight good practice and pitfalls in the design and manufacture of TMAs. Issues, such as the size, number, spacing and layout of cores, as well as the assessment and reporting of studies using TMAs are addressed. We make some suggestions regarding these challenges, and propose a checklist of features that should be considered in order to stimulate debate and improve the quality of data produced by TMA analysis.
Do state breastfeeding laws in the USA promote breast feeding?
Authors: Hawkins Summer Sherburne , Stern Ariel Dora , Gillman Matthew W
Published: October 2012

Objectives

Despite the passage of state laws promoting breast feeding, a formal evaluation has not yet been conducted to test whether and/or what type of laws may increase breast feeding. The enactment of breastfeeding laws in different states in the USA creates a natural experiment. We examined the impact of state breastfeeding laws on breastfeeding initiation and duration as well as on disparities in these infant feeding practices.

Methods

Using data from the Pregnancy Risk Assessment Monitoring System, we conducted differences-in-differences models to examine breastfeeding status before and after the institution of laws between 2000 and 2008 among 326 263 mothers from 32 states in the USA. For each mother, we coded the presence of two types of state breastfeeding laws. Mothers reported whether they ever breast fed or pumped breast milk (breastfeeding initiation) and, if so, how long they continued. We defined breastfeeding duration as continuing to breast feed for ≥4 weeks.

Results

Breastfeeding initiation was 1.7 percentage points higher in states with new laws to provide break time and private space for breastfeeding employees (p=0.01), particularly among Hispanic mothers (adjusted coefficient 0.058). While there was no overall effect of laws permitting mothers to breast feed in any location, among Black mothers we observed increases in breastfeeding initiation (adjusted coefficient 0.056). Effects on breastfeeding duration were in the same direction, but slightly weaker.

Conclusions

State laws that support breast feeding appear to increase breastfeeding rates. Most of these gains were observed among Hispanic and Black women and women of lower educational attainment suggesting that such state laws may help reduce disparities in breast feeding.
Embolization of the deep cervical collaterals—a unique endovascular approach to prevent repeated posterior fossa strokes refractory to medical therapy
Authors: Mammen Thomas , Vosoughi Reza , Wadhwa Vikram
Published: October 2012

We present a 69-year-old man with advanced vertebral artery atherosclerotic disease and repeated posterior fossa strokes, refractory to aggressive medical treatment. CT angiogram showed heavily calcified long segment occlusion of the dominant right vertebral artery. Beyond the occlusion, the vertebral artery was reconstituted by hypertrophic deep cervical collaterals which had multiple long and short segments of severe stenosis and antegrade flow. The ostium of the right vertebral artery was heavily calcified, and multiple attempts to catheterize the vertebral artery were unsuccessful. Flow reversal was eventually achieved in the right vertebral artery by embolizing the hypertrophied deep cervical artery which reconstituted the right vertebral artery. The patient has remained asymptomatic since the procedure for a follow-up period of 12 months.
Pain assessment in neonates and infants in the post-operative period following cardiac surgery
Authors: Cury Mariana R J , Martinez Francisco E , Carlotti Ana P C P
Published: October 2012

Purpose

We aimed to test the convergent validity of the COMFORT scale and the Cardiac Analgesic Assessment Scale (CAAS) and to evaluate changes in physiological parameters over time in response to a painful procedure in neonates and infants following cardiac surgery.

Methods

From October 2006 to May 2008, 16 children were prospectively evaluated over 1–3 days after cardiac surgery while they remained on mechanical ventilation and received infusions of sedatives and analgesics. Pain was assessed by the COMFORT scale and CAAS before and during endotracheal tube suctioning. Heart rate, systemic systolic blood pressure, pulmonary artery pressure, oxygen saturation and pupil size were recorded at the same times.

Results

During endotracheal suctioning on the first day, there was a significant increase in COMFORT and CAAS scores, systemic systolic blood pressure tended to decrease, pulmonary artery pressure significantly increased and there was a significant reduction in oxygen saturation. Heart rate and pupil size did not change significantly during the painful procedure throughout the study. COMFORT scores significantly correlated with CAAS scores on all days. Nevertheless, agreement for the detection of pain between both scales was weak (κ<0.5). The COMFORT scale detected more patients with pain.

Conclusions

There was poor agreement between the COMFORT scale and CAAS for detection of pain in neonates and infants who had undergone cardiac surgery. A reduction in systemic systolic blood pressure and a rise in pulmonary artery pressure were observed during painful stimulation on the first post-operative day. For this population, a pain scale scoring physiological parameters according to their variation to higher and lower values should be developed.
THE LOCALLY OPTIMAL STRUCTURE FOR SYNCHRONIZABILITY OF DYNAMICAL NETWORKS
Authors: BU SHOULIANG , WEN JIAN-PING , ZHONG QING-HU , YI XUE-HUA
Published: October 2012

A network is referred to have locally optimal structure for synchronizability if its synchronizability is always decreased, no matter an arbitrary edge is added to it or an arbitrarily existed edge is deleted from it or an arbitrary edge is rewired in it. Although it is difficult to generally determine which networks have locally optimal structure, this paper through various examples demonstrates that symmetrical networks indeed have this property. Actually, it is found that any structural perturbations which destruct the symmetry of an originally symmetrical network would decrease the network's synchronizability, no matter how the perturbations change the network's average path length or clustering coefficient.
A COMPARATIVE STUDY FOR TWO-DAMAGE MODELLING MODELS USING COMPOSITE MATERIAL
Authors: CHEBBI EL. , JARRAYA A. , DAMMAK F.
Published: October 2012

Purpose- This paper describes finite element fatigue damage modeling.

Design/Methodology/Approach- Fatigue life prediction and damage progressive evaluation are analytically studied. We present a numerical implementation of the studied models into the home made finite element code MPEF. Numerical simulations are performed on composite and metallic material. We carried out a parametric study to investigate the influence of model's parameters on the damage accumulation and their sensitivity on its kinetics. Simulations are conducted for two different loading levels to characterize cumulative damage and to study loading sequence effect. A comparative study is performed to characterize the efficiency of the two models to describe the damage evolution for the two different materials.

Findings- Numerical examples are presented to illustrate its performance.

Originality/value- This paper intends to present a comparative study of the damage evolution for metallic and composite material under uniaxial loading. The effect of the loading sequence will be investigated.
TUNABLE BAND STRUCTURES OF 2D MULTI-ATOM ARCHIMEDEAN-LIKE PHONONIC CRYSTALS
Authors: XU Y. L. , CHEN C. Q. , TIAN X. G.
Published: October 2012

Two dimensional multi-atom Archimedean-like phononic crystals (MAPCs) can be obtained by adding "atoms" at suitable positions in primitive cells of traditional simple lattices. Band structures of solid-solid and solid-air MAPCs are computed by the finite element method in conjunction with the Bloch theory. For the solid-solid system, our results show that the MAPCs can be suitably designed to split and shift band gaps of the corresponding traditional simple phononic crystal (i.e., with only one scatterer inside a primitive cell). For the solid-air system, the MAPCs have more and wider band gaps than the corresponding traditional simple phononic crystal. Numerical calculations for both solid-solid and solid-air MAPCs show that the band gap of traditional simple phononic crystal can be tuned by appropriately adding "atoms" into its primitive cell.
NUMERICAL MODELING OF THE FRACTURE BEHAVIOR OF OPEN CELL FOAMS
Authors: JIN Y. J. , WANG T. J.
Published: October 2012

The objective of this work is to numerically study the individual and mixed mode fracture behavior of open-cell foams. Three-dimensional tetrakaidecahedron model is adopted and finite element method is employed in analysis. The overall elastic properties of open-cell foams are numerically obtained. Then, modes I, II, III and mixed mode I–II fracture behavior of open-cell foams are numerically predicted respectively, in which both solid/hollow and square/circular strut cross-sections are considered. It is seen that the relationship between the overall critical stress intensity factor and the relative density of foam obeys power law for individual crack problems. Effects of the shape and the topology of strut cross-section are discussed in detail. For mixed mode I–II crack problem, the relationship between KI/KICand KII/KIICis obtained and the effect of the shape of strut cross-section is discussed.
Advanced Modelling of Silicon Wafer Solar Cells
Authors: Peters Marius , Fajun Ma , Siyu Guo , Hoex Bram , Blaesi Benedikt , Glunz Stefan , Aberle Armin , Luther Joachim
Published: October 2012

Modelling of solar cells today is general practice in research and widely-used in industry. Established modelling software is typically limited to one dimension and/or to small scales. Additionally, novel effects, like, e.g., the use of diffractive structures or luminescent materials, are not established. In this paper we discuss how the combination of different modelling techniques can be used to overcome these limitations. In this context two examples are presented. The first example concerns the combination of the open source simulation software PC1D with circuit modelling to investigate the effect of local shunts on the global characteristics of a silicon wafer solar cell. For the investigated example (4.5 cm2 cell area) we find that a local point shunt reduces the solar cell efficiency by 4% relative. The second example concerns the modelling of diffractive gratings for thin silicon wafer solar cells. For this purpose, we use the rigorous coupled wave analysis to simulate Sentaurus technical computer-aided design (TCAD) is combined with the rigorous coupled wave analysis, a method to solve Maxwell's equations for periodic structures. Here we show that a grating can be used to improve the absorption in a thin silicon wafer solar cell considerably.
Low-Temperature Back-Surface-Field Structures Applied to Crystalline Silicon Solar Cells: Two-Step Growth with Hydrogen Plasma Treatment for Improving the Reproducibility
Authors: Sakata Isao , Yamanaka Mitsuyuki , Takato Hidetaka , Kawanami Hitoshi
Published: October 2012

We sometimes observe poor internal quantum efficiency (IQE) in the long-wavelength region of p-type single-crystalline silicon (c-Si) solar cells having back-surface-field (BSF) layers made of p-type hydrogenated amorphous silicon (a-Si:H). We found that this poor IQE is caused by the appearance of a polycrystalline phase (PP) in a-Si:H. We showed that two-step growth of BSF structures with hydrogen plasma treatment (HPT) is effective for achieving a high performance of BSF with improved reproducibility. First, a-Si:H layers were prepared on c-Si substrates at a high growth rate to suppress the appearance of PP, and consequently, the defects at the a-Si:H/c-Si interface induced by the higher growth rate were effectively passivated by HPT. Finally, a-Si:H was deposited as a capping layer on the first a-Si:H layer after HPT. We will discuss the passivation mechanism of interface defects with HPT using the data of the hydrogen profile in the a-Si:H layers treated by hydrogen plasma.
Improved Electronic Properties of Laser-Doped Emitters by Reducing Surface Roughness
Authors: Nishimura Hideki , Hirata Kenji , Hasegawa Mitsuhiro , Katagiri Takuya , Fuyuki Takashi
Published: October 2012

Laser doping (LD) can help form emitters at low cost and in high throughput because it operates in air atmosphere and at room temperature. Moreover, LD makes high-efficiency structures in a very simple way by melting and diffusing impurities on selective areas. In this study, evaluation of the relationship between multicrystalline silicon (mc-Si) surface conditions and electric properties is carried out. The results show that the surface electric properties were improved and conversion efficiencies were increased. This was accomplished by changing the surface conditions from rough to smooth by surface etching and vacuum treatment before LD.
Large-Grain Polycrystalline Silicon Films Formed through Flash-Lamp-Induced Explosive Crystallization
Authors: Ohdaira Keisuke , Sawada Keisuke , Usami Noritaka , Varlamov Sergey , Matsumura Hideki
Published: October 2012

The flash lamp annealing (FLA) of electron-beam- (EB-) evaporated amorphous silicon (a-Si) films results in the formation of polycrystalline Si (poly-Si) films with at least a few µm long grains stretching along lateral crystallization directions. Unlike the case of using chemical-vapor-deposited (CVD) hydrogenated a-Si films as precursors, no peeling of Si films occurs even in the absence of Cr adhesion layers. Such a flash-lamp-induced crystallization occurs also in doped EB-evaporated a-Si films as in the case of undoped films. The p+/p-/n+ stacked structure is sufficiently kept even after crystallization, although the profiles of dopants are slightly modified. This fact clearly indicates that the crystallization observed is not based on liquid-phase epitaxy (LPE) after the complete melting of the whole a-Si precursor during millisecond-order treatment but through LPE-based explosive crystallization (EC), self-catalytic lateral crystallization driven by the release of latent heat. The formation of poly-Si films with large grains and the sufficient preservation of dopant profiles would lead to the utilization of the poly-Si films formed for solar cell devices.
Graded Layer Modification for High Efficiency Hydrogenated Amorphous Silicon–Germanium Solar Cells
Authors: Chung Jin-Won , Park Jun Woong , Lee Yu Jin , Ahn Seh-Won , Lee Heon-Min , Park O Ok
Published: October 2012

Hydrogenated amorphous silicon–germanium (a-SiGe:H) solar cells are fabricated with different thicknesses of the i/n graded layer and profiling shapes for appropriate band gap profiling. Comparison of the solar parameters between the U-shape profiling and the exponential shape (E-shape) profiling has been carried out at the same total thickness. In the U-shape profiling, as the thickness of the i/n graded layer increase, the fill factor (FF) and open circuit voltage (V
oc) of p–i–n single-junction a-SiGe:H solar cells increase, but the short circuit current (J
sc) of cells decreases. In the E-shape profiling, the J
sc of the a-SiGe:H cell is enhanced without significant losses in V
oc. For further analysis, a modified E-shape profiling is incorporated in a-Si:H/a-SiGe:H double-junction cells, which has resulted in the improvement of V
oc and FF of double-junction cells to 1.67 V and 0.753, respectively, without significant reduction in J
scSiGe
QE, 12.58 mA/cm2.
Influence of Mo Back-Contact Oxidation on Properties of CIGSe2 Thin Film Solar Cells on Glass Substrates
Authors: Rissom Thorsten , Kaufmann Christian A. , Caballero Raquel , Schniebs Jan , Schock Hans-Werner , Wiedenbeck Michael
Published: October 2012

Copper indium gallium diselenide (CIGSe) solar cells grown on glass substrates have reached an efficiency of 20.3%. Their industrial production is becoming increasingly relevant. While various deposition techniques for the fabrication of the absorber are used by different groups and corporations, molybdenum (Mo) has become the back contact material of choice. Oxidation of the bare Mo layer prior to absorber deposition is a phenomenon that is generally hard to control or to avoid. Since the incorporation of sodium (Na) into the absorber layer is commonly achieved by diffusion from a glass substrate through the Mo layer, oxidation of the back contact will influence the diffusion, and thus the availability of Na during the CIGSe growth process. In order to investigate this effect, Na containing glass substrates with Mo layers in different stages of oxidation have been prepared using a damp heat treatment. The samples were coated with CIGSe by physical vapor deposition in a multistage co-evaporation process. The CIGSe/Mo-interface is investigated by Raman spectroscopy and secondary ion mass spectroscopy, using a lift-off technique. The damp heat treatment led to the formation of an oxide layer (presumably MoO2) and an increase of the sodium content in the grown absorber layers.
Fabrication and Characterization of Cu(In,Ga)(S,Se)2-Based Solar Cells
Authors: Komaki Hironori , Iioka Masayuki , Yamada Akimasa , Furue Shigenori , Ishizuka Shogo , Matsubara Koji , Shibata Hajime , Niki Shigeru
Published: October 2012

We formed Cu(In,Ga)(S,Se)2 films using a three-stage process. The grain size of the films was reduced by increasing their S concentration. Judging from the phase diagrams of Cu–S and Cu–Se, a decrease in grain size with the increase in S concentration may be due to the higher the melting point of Cu2S compared to that of Cu2Se. The short circuit current density of the fabricated solar cells decreased significantly with an increase in S concentration. Secondary ion mass spectrometry showed an unsuitable compositional distribution of S and Se despite the constant S/Se flux ratio during growth. A maximum open circuit voltage of 0.83 V was obtained at a S/(S+Se) ratio of 0.80 in the fabricated solar cells in order to increase bandgap.
Growth of Ag(In,Ga)Se2 Films by Modified Three-Stage Method and Influence of Annealing on Performance of Solar Cells
Authors: Xianfeng Zhang , Kobayashi Tsuyoshi , Kurokawa Yasuyoshi , Yamada Akira
Published: October 2012

A modified three-stage method was introduced to deposit high-efficiency Ag(In,Ga)Se2 (AIGS) solar cells. Cu(In,Ga)Se2 (CIGS) and AIGS films were deposited by conventional and modified three-stage methods, respectively, to enable a comparison of the diffusion processes of Ag and Cu into (In,Ga)2Se3 films during the second stage. The diffusion coefficient of Ag is less than that of Cu, causing the easy segregation of Ag in the film. High-temperature annealing could improve the diffusion coefficient of Ag, consequently improving the solar cell performance. Air annealing of the AIGS solar cell can also improve the cell performance significantly, and finally an efficiency of 9.2% was achieved.
First-Principles Study on Cd Doping in Cu2ZnSnS4 and Cu2ZnSnSe4
Authors: Maeda Tsuyoshi , Nakamura Satoshi , Wada Takahiro
Published: October 2012

To quantitatively evaluate the substitution energies of Cd atom for Cu, Zn, or Sn atom in indium-free photovoltaic semiconductors Cu2ZnSnS4 (CZTS) and Cu2ZnSnSe4 (CZTSe), first-principles pseudopotential calculations using plane-wave basis functions were performed. The substitution energies of Cd atom in kesterite-type CZTS and CZTSe were calculated in consideration of the atomic chemical potentials of the constituent elements of Cu, Zn, Sn, and the doping atom of Cd. During the chemical bath deposition (CBD) of the CdS layer on the CZTS or CZTSe layer, Cu, Zn, and Cd atoms dissolved in the ammonia aqueous solution and formed [Cu(NH3)2]+, [Zn(NH3)4]2+, and [Cd(NH3)4]2+ complex ions. Therefore, the chemical potentials of Cu, Zn, and Cd atoms in [Cu(NH3)2]+, [Zn(NH3)4]2+, and [Cd(NH3)4]2+ complex ions were calculated. We found that the substitution energies of n-type CdCu and charge-neutral CdZn in CZTS and CZTSe are smaller than that of p-type CdSn. The substitution energies of CdCu in CZTS and CZTSe are smaller than that in chalcopyrite-type CuInSe2 (CIS). However, the substitution energies of CdCu, CdZn, and CdSn are positive values. The formation energy of charge-neutral Cd doping with the Cu vacancy (CdCu + VCu) pair is a negative value and greatly smaller than those of donor-type CdCu and neutral CdZn in CZTS and CZTSe. These results indicate that the charge-neutral (CdCu + VCu) vacancy pair is easily formed during the CBD of the CdS layer on the CZTS or CZTSe layer. A small amount of n-type CdCu and neutral CdZn would also be formed.
Fabrication of Cu2ZnSnS4 Thin Film Solar Cell Using Single Step Electrodeposition Method
Authors: Pawar Sambhaji M. , Pawar Bharati S. , Gurav Kishor V. , Bae Do Won , Kwon Se Han , Kolekar Sanjay S. , Kim Jin Hyeok
Published: October 2012

Cu2ZnSnS4 (CZTS) thin films were deposited onto Mo-coated and tin-doped indium oxide (ITO) coated glass substrates by using single step electrodeposition technique followed by annealing in N2 + H2S atmosphere. Subsequently, they were applied to the fabrication of thin film solar cells. Upon annealing, the amorphous nature of as-deposited precursor film changes into polycrystalline kesterite crystal structure with uniform and densely packed surface morphology. Energy dispersive X-ray spectroscopy (EDS) study reveals that the deposited thin films are nearly stoichiometric. Optical absorption study shows the band gap energy of as-deposited CZTS thin films is 2.7 eV whereas, after annealing, it is found to be 1.53 eV. The solar cell fabricated with CZTS absorber layer, showed the best conversion efficiency (η) 1.21% for 0.44 cm2 with open-circuit voltage (V
oc) = 315 mV, short-circuit current density (J
sc) = 12.27 mA/cm2 and fill factor (FF) = 0.31.
Preparation of Cu2SnS3Thin Films by Sulfurization of Cu/Sn Stacked Precursors
Authors: Chino Kotaro , Koike Junpei , Eguchi Shinya , Araki Hideaki , Nakamura Ryota , Jimbo Kazuo , Katagiri Hironori
Published: October 2012

Cu2SnS3(CTS) has been reported to have various band gap energies in the range of 0.93–1.77 eV and an absorption coefficient of 1.0×104cm-1. It consists of elements that are inexpensive due to their abundance in Earth's crust. Consequently, CTS is expected to be utilized in the absorber layers of thin-film solar cells. In this study, Cu/Sn stacked-layer thin-film precursors were deposited on glass and glass/Mo substrates by electron beam evaporation. CTS thin films were fabricated by sulfurizing the precursors at temperatures of 450–580 °C for 2 h in an atmosphere of N2and sulfur vapor. CTS films were estimated to have band gap energies of 0.96–1.00 eV by extrapolation. A solar cell fabricated using a CTS thin film sulfurized at 580 °C exhibited an open-circuit voltage of 211 mV, a short-circuit current of 28.0 mA/cm2, a fill factor of 0.43, and a conversion efficiency of 2.54%.
Structural, Optical, and Electro-Optical Properties of Thermally Evaporated Tin Sulphide Layers
Authors: Nwofe Patrick A. , Reddy K. T. Ramakrishna , Sreedevi G. , Tan John K. , Miles Robert W.
Published: October 2012

Thin films of tin sulphide (SnS) were deposited onto glass substrates using the thermal evaporation method. The substrate temperature, T
s was varied in the range, 280–360 °C, keeping other growth parameters constant and the effects on the chemical and physical properties of the layers deposited were investigated. The layers were observed to consist of densely packed grains, up to 9.5 µm in diameter, and X-ray diffraction studies showed the layers had a strong preferred (040) orientation. The energy band gap, determined from optical studies was found to be in the range 1.30–1.34 eV, while the optical absorption coefficient was found to be >104 cm-1 for photons with energies greater than the energy bandgap. The electrical resistivity of the films decreased with an increase of substrate temperature. Heterojunction devices were made using chemical bath deposited cadmium sulphide (CdS) as the window layer and the minority carrier diffusion length in the SnS measured to be 0.23 µm using spectral response studies.
Extension of Absorption Wavelength in GaAs/AlGaAs Quantum Dots with Underlying Quantum Well for Solar Cell Application
Authors: Elborg Martin , Noda Takeshi , Mano Takaaki , Jo Masafumi , Ding Yi , Sakoda Kazuaki
Published: October 2012

We fabricated a GaAs/AlGaAs quantum dot solar cell (QD-SC) in which GaAs QDs with an underlying quantum well (QW) layer were grown to enable the absorption of long-wavelength photons. Photoluminescence emission of these QDs with an underlying QW, referred to as QDW structure, is redshifted and significantly narrower than that of plain QDs. The extension of absorption wavelength is clearly observed in the spectral response of the samples while keeping zero-dimensional confinement as confirmed by calculation. Improvement in fill factor in the QDW sample compared with plain QDs is demonstrated.
Composite Films Based on Poly(3,4-ethylene dioxythiophene):Poly(styrene sulfonate) Conducting Polymer and TiC Nanoparticles as the Counter Electrodes for Flexible Dye-Sensitized Solar Cells
Authors: Yeh Min-Hsin , Lin Lu-Yin , Li Yu-Yan , Chang Jeffrey , Chen Ping-Wei , Lee Chuan-Pei , Ho Kuo-Chuan
Published: October 2012

A composite film of poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) and titanium carbide nanoparticles (TiC-NPs) was deposited on an indium doped tin oxide–poly(ethylene naphthalate) (ITO–PEN) conducting plastic substrate by a doctor blade technique. This ITO–PEN substrate with the composite film was used as the flexible counter electrode (CE) for a plastic dye-sensitized solar cell (DSSC). Performances of the plastic DSSC with the platinum-free CEs containing PEDOT:PSS/TiC-NPs composite was investigated. A solar-to-electricity conversion efficiency (η) of 6.50% was achieved for the pertinent DSSC with PEDOT:PSS/TiC-NPs composite, using commercial N719 dye, which exhibited comparable performance to that of a cell with a sputtered-Pt film on its CE (6.84%). The homogeneous nature of the composite film PEDOT:PSS/TiC-NPs, the uniform distribution of TiC-NPs in its PEDOT:PSS matrix, and the large electrochemical surface area of the composite film are seen to be the factors for the best performance of the pertinent DSSC. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) were used to characterize the TiC-NPs. Scanning electron microscopy (SEM), atomic force microscopy (AFM), and energy dispersive X-ray spectroscopy (EDX) were used to characterize the films. The high efficiency of the cell with PEDOT:PSS/TiC-NPs is explained by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and incident photon-to-current conversion efficiency (IPCE) curves.
Evaluation of Microscopic Properties of Organic Solar Cells by Light-Induced Electron Spin Resonance
Authors: Marumoto Kazuhiro , Nagamori Tatsuya
Published: October 2012

We have investigated organic thin-film solar cells from the microscopic viewpoint with light-induced electron spin resonance (ESR). The utilized cell structures are indium–tin oxide (ITO)/poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS)/regioregular poly(3-hexylthiophene) (P3HT):[6,6]-phenyl C61-butyric acid methylester (PCBM)/Pd/LiF/Al. We performed simultaneous measurements of light-induced ESR and device characteristics using the same device. Under simulated solar irradiation, the light-induced ESR intensity of a solar cell increases, while the short-circuit current and open-circuit voltage of the cell concomitantly decrease with increasing duration of irradiation. We have successfully observed a clear correlation between the light-induced ESR intensity and the device characteristics. Trapping sites of photogenerated hole carriers (positive polarons) are ascribed to P3HT by the analysis of the ESR signals.