Cap Method Research Articles

Iron Sulfide Minerals as Potential Active Capping Materials for Mercury-Contaminated Sediment Remediation: A Minireview

Several innovative approaches have been proposed in recent years to remediate contaminated sediment to reduce human health and environmental risk. One of the challenges of sediment remediation stems from its unfeasible high cost, especially when ex situ strategies are selected. Therefore, in situ methods such as active capping have been emerging as possible options for solving sediment problems. Active capping methods have been extensively tested in field-scale sediment remediation for organic pollutants (e.g., PCBs, PAHs, DDT) contamination with good sequestration efficiency; however, these methods have not been widely tested for control of heavy metal pollutants, such as mercury (Hg). In this review, the potentials of using iron sulfide minerals to sequestrate Hg were discussed. Iron sulfide minerals are common in the natural environment and have shown good effectiveness in sequestrating Hg by adsorption or precipitation. Iron sulfides can also be synthesized in a laboratory and modified to enhance their sequestration ability for Hg. Some of the potential advantages of iron sulfides are pointed out here. Additional tests to understand the possibility of applying iron sulfides as active caps to remediate complicated environment systems should be conducted.

Research of Focal Mechanism and Focal Depth of Qilian, QinghaiMs5.2 Earthquake

This paper selects the waveform records of 16 broadband digital seismic stations in the regional seismic network of Gansu province, Qinghai province, and Sichuan province involved inversion, use CAP focal mechanism solution method to calculate the Ms 5.2 earthquake which occurred in Qilian County, Qinghai Province, November 23, 2015. Obtained the focal mechanism solution of this earthquake is a strike-slip fault with thrust property. The inversion results show the optimal double couple solution is nodal plane I: The strike is 112°, the dip, 51.7°; and the rake, 24.5°. Nodal plane II: The strike is 7°, the dip, 71°; and the rake, 139°. Earthquake moment magnitude isMw5.2 and the optimal depth solution is 8km, which is consistent with the results of IGP-CEA. We calculate focal depth with the arrival time difference between sPn and Pn phases, the results is 6.6km, which agree with the CAP method results and verify the feasibility of this method.

Focal depth of the Yunnan Jinggu <italic>M</italic><sub>w</sub>6.1 earthquake: Discussion on depth of the brittle-ductile transition zone of a young fault

Since most continental earthquakes occur in the brittle layer instead of ductile layers, the focal depth of an earthquake provides an important constraint on the rheology structure of fault zone. According to the results of previous studies, the typical depth of brittle-ductile transition zone on mature faults is about 10 km. However, several moderate earthquakes occurred on young faults in stable cratons, and focal depths of those events are very shallow (e.g. the 1993 M w6.1 India Killari earthquake and a series of shallow earthquakes in Australia). Those observations suggest that depth of the brittle- ductile zone on young faults in cratons is shallower than that on mature faults. In this study, we report a case on a young fault in a tectonically active region that has not been well studied and discuss implications for the rheology structure. On October 7, 2014, an M w6.1 earthquake occurred in Jinggu, Yunnan (China), the southeastern part of the tectonically active Yunnan-Myanmar block, followed by two aftershocks of M >5 in December. According to historical seismicity and geologic studies in this region, it is suggested that the seimogenic fault of the Jinggu earthquake is a young fault. We use data from global and regional seismic networks, as well as aftershock data from the Lozhadu reservoir network and temporary stations, to study focal depths of the mainshock and aftershocks. The hypocenter of a reference event ( M w4.3) that was recorded with two close temporary stations is determined, and then the hypocenters of the mainshock and two moderate aftershocks are relocated with a relative method based on Pn/Pg arrival times. The relocated hypocenter of the mainshock is 9.5 km deep, whereas the hypocenters of the two aftershocks are about 10 km deep. The centroid depth is investigated with the CAP method based on waveform modeling. Both teleseismic and regional waveforms are used to invert for the centroid depth of the mainshock. The optimal waveform fit is obtained with a depth of 5 km. The two aftershocks are studied with regional waveforms only and the results are close to the hypocenter depths. Since the hypocenter indicates the initial point of rupture whereas the centroid location is close to the center of the main rupture patch, we propose the mainshock initiated at 10 km depth and expanded to the brittle layer at shallower depth. For two aftershocks, the consistency of hypocenter depth and centroid depth suggests circular rupture patterns. Therefore, we propose the bottom of the seismogenic layer and brittle-ductile transition zone is about 10 km deep. This hypothesis is also supported by other observations. Magnetotelluric study in this region reveals a low conductivity layer above 10 km that is regarded as brittle rock, whereas the high conductivity layer beneath 15 km is regarded as ductile rock. Furthermore, a regional rheology model, which is obtained with surface temperature, seismic velocity, and GPS data, also suggests the brittle-ductile transition zone is at about 9 km depth. In summary, the depth of the brittle-ductile transition zone on the young fault in the tectonic active region is similar to that of mature faults, which is useful information for lithosphere geodynamics studies.

Best practices for pervious concrete mix design and laboratory tests

Abstract Pervious concrete may be used for stormwater management since it allows the water to pass through its interconnected macropores into stormwater systems or soils below. However, there is a need for additional standards related to pervious concrete prior to its widespread use, and there are many aspects related to mix design for desired properties, compaction methods, and test procedures that are not yet completely understood. These variables may significantly affect the functional and mechanical performance of the material. In this paper, mix designs and test specimen preparation techniques were evaluated. The IBRACON method for mixture design was used to obtain the mixture proportions and the calculated density for the desired porosity of 25%. In addition, two different types of specimens (cast or cored) and compaction methods (roller or Proctor hammer compacted) were performed. The density of each specimen was controlled to obtain the same calculated density. Several tests were conducted to compare the following variables: density, porosity, surface infiltration rate, permeability and compressive strength. Additionally, the effects of mortar capping versus neoprene-rubber caps on compressive strength measurements of pervious concrete were evaluated. The experimental results showed that cast specimens have more consistent results than cores. The design method studied with strict control of density was efficient to obtain the desired porosity mainly for cast specimens. The roller leads to a more compacted top surface resulting in a decrease in the infiltration rate and permeability of the cores. The mortar capping method is more consistent than the other.

An Ab Initio QM/MM Study of the Electrostatic Contribution to Catalysis in the Active Site of Ketosteroid Isomerase.

The electric field in the hydrogen-bond network of the active site of ketosteroid isomerase (KSI) has been experimentally measured using vibrational Stark effect (VSE) spectroscopy, and utilized to study the electrostatic contribution to catalysis. A large gap was found in the electric field between the computational simulation based on the Amber force field and the experimental measurement. In this work, quantum mechanical (QM) calculations of the electric field were performed using an ab initio QM/MM molecular dynamics (MD) simulation and electrostatically embedded generalized molecular fractionation with conjugate caps (EE-GMFCC) method. Our results demonstrate that the QM-derived electric field based on the snapshots from QM/MM MD simulation could give quantitative agreement with the experiment. The accurate calculation of the electric field inside the protein requires both the rigorous sampling of configurations, and a QM description of the electrostatic field. Based on the direct QM calculation of the electric field, we theoretically confirmed that there is a linear correlation relationship between the activation free energy and the electric field in the active site of wild-type KSI and its mutants (namely, D103N, Y16S, and D103L). Our study presents a computational protocol for the accurate simulation of the electric field in the active site of the protein, and provides a theoretical foundation that supports the link between electric fields and enzyme catalysis.

A mild capping method for SPPS on the N-methyl diaminobenzoyl linker: Synthesis of an N-acyl urea appended C. elegans neuropeptide

In this manuscript, we establish the susceptibility of the N-methyldiaminobenzoyl linker to undergo undesired acylation during standard peptide capping with acetic anhydride. Successive capping treatments led to problematic levels of linker incapacitation. We describe a mild, inexpensive alternative capping strategy that is completely selective for the N terminus with no acylation of the linker detected for any of the substrates evaluated. The utility of this protocol is demonstrated via the synthesis of the CAPA-PVK-1 consensus sequence of the C. elegans neuropeptide-like protein precursor peptide NLP-44.

Supramolecular Nanosystem Based on Pillararene-Capped CuS Nanoparticles for Targeted Chemo-Photothermal Therapy.

A smart supramolecular nanosystem integrating targeting, chemotherapy, and photothermal therapy was constructed based on carboxylatopillar[5]arene (CP[5]A)-functionalized CuS nanoparticles (CuS@CP NPs). CuS@CP NPs with good monodispersibility and strong near-infrared absorption were synthesized in aqueous solution through a facile one-pot supramolecular capping method, followed by surface installation of a liver cancer-targeted galactose derivative through host-guest binding interaction. The resulting smart supramolecular nanosystem, namely, CuS@CPG, exhibited excellent photothermal ablation capability to HepG2 cells upon irradiation with laser at 808 nm. Chemotherapeutic drug, doxorubicin hydrochloride (DOX), was further loaded on CuS@CPG via electrostatic interactions between positively charged DOX and negatively charged CP[5]A to give CuS@CPG-DOX with a high drug-loading capacity up to 48.4%. The weakening of DOX-CP[5]A interactions in an acidic environment promoted the pH-responsive drug release from CuS@CPG-DOX. Significantly, this multifunctional supramolecular nanosystem showed a remarkably enhanced therapeutic effect through the combination of targeted chemotherapy and photothermal therapy upon in vitro cell study. Moreover, preliminary in vivo study demonstrated that CuS@CPG and CuS@CPG-DOX had good biocompatibility and excellent tumor inhibition effects upon near-infrared laser irradiation.

Association of Uveal Melanoma Metastatic Rate With Stochastic Mutation Rate and Type of Mutation

It is necessary to understand the mechanisms of metastasis of uveal melanoma to advise patients and develop treatments for this tumor. To examine the stochastic properties of primary uveal melanoma including the mutation rate as a function of tumor size and metastatic rate relative to the type of mutation. We computed the mutation rate in different sized uveal melanomas using previously published large data sets. Tumor volume was estimated using the spherical cap method. We also calculated the metastatic rate using an updated data set of patients with uveal melanoma with known mutations in BAP1, SF3B1, and EIF1AX provided by the Rotterdam Ocular Melanoma Study Group. Data were analyzed from 2 studies, one taking place from August 25, 1970, to August 27, 2008, and the other taking place between 1993 and 2013. Data were analyzed between 2016 and 2017. Mutation rates and metastic rates. Based on the 5-year metastatic rates, mutation rates ranged from 1.09 × 10-8 to 7.86 × 10-7 per cell division, using our calculation algorithm. A higher mutation rate was found for tumors with smaller thicknesses. EIF1AX mutations were not exclusive of other mutations because 2 cases with EIF1AX mutations and metastasis also had BAP1 mutations. None of the tumors with only an EIF1AX mutation metastasized. After plotting the yearly metastatic rate vs time after treatment, we observed a small peak at 1 year and a large peak at 3.5 years after treatment for BAP1 mutations, with peaks between 2 and 3 years and at 7 years for SF3B1 mutations. We observed a higher mutation rate for smaller tumors, which may be explained by a greater number of cell divisions occurring during the expansion phase of smaller uveal melanomas. Regarding time to clinically detected metastases, the first 2 peaks appear to be associated with BAP1-mutated tumors and the late peak to SF3B1-mutated tumors.

Contact angle measurement in lattice Boltzmann method

Contact angle is an essential characteristic in wetting, capillarity and moving contact line; however, although contact angle phenomena are effectively simulated, an accurate and real-time measurement for contact angle has not been well studied in computational fluid dynamics, especially in dynamic environments. Here, we design a geometry-based mesoscopic scheme for on-the-spot measurement of the contact angle in the lattice Boltzmann method. The measuring results without gravity effect are in good agreement with the benchmarks from the spherical cap method. The performances of the scheme are further verified in gravitational environments by simulating sessile and pendent droplets on smooth solid surfaces and dynamic contact angle hysteresis on chemically heterogeneous surfaces. This scheme is simple and computationally efficient. It requires only the local data and is independent of multiphase models.

Uridine Depletion and Chemical Modification Increase Cas9 mRNA Activity and Reduce Immunogenicity without HPLC Purification

The Cas9/guide RNA (Cas9/gRNA) system is commonly used for genome editing. mRNA expressing Cas9 can induce innate immune responses, reducing Cas9 expression. First-generation Cas9 mRNAs were modified with pseudouridine and 5-methylcytosine to reduce innate immune responses. We combined four approaches to produce more active, less immunogenic second-generation Cas9 mRNAs. First, we developed a novel co-transcriptional capping method yielding natural Cap 1. Second, we screened modified nucleotides in Cas9 mRNA to identify novel modifications that increase Cas9 activity. Third, we depleted the mRNA of uridines to improve mRNA activity. Lastly, we tested high-performance liquid chromatography (HPLC) purification to remove double-stranded RNAs. The activity of these mRNAs was tested in cell lines and primary human CD34+ cells. Cytokines were measured in whole blood and mice. These approaches yielded more active and less immunogenic mRNA. Uridine depletion (UD) most impacted insertion or deletion (indel) activity. Specifically, 5-methoxyuridine UD induced indel frequencies as high as 88% (average ± SD = 79% ± 11%) and elicited minimal immune responses without needing HPLC purification. Our work suggests that uridine-depleted Cas9 mRNA modified with 5-methoxyuridine (without HPLC purification) or pseudouridine may be optimal for the broad use of Cas9 both in vitro and in vivo.

Virola oleifera-capped gold nanoparticles showing radical-scavenging activity and low cytotoxicity

The development of effective nanoparticle therapeutics has been hindered by their surface characteristics, such as hydrophobicity and charge. Therefore, the success of biomedical applications with nanoparticles is governed by the control of these characteristics. In this article, we report an efficient green capping method for gold nanoparticles (AuNPs) by a reduction with sodium citrate and capping with Virola oleifera (Vo), which is a green exudate rich in polyphenols and flavonoids. The Vo-capped AuNPs were characterized by UV, DLS, FTIR, Raman, TEM, DPPH, FRAP and their cytotoxicity was evaluated on the viability of Murine macrophage cell. The AuNPs had an average particle size of 15 nm and were stable over a long time, as indicated by their unchanged SPR and zeta potential values. These nanoparticles were assessed for their antioxidant potential using DPPH and FRAP and demonstrated the highest antioxidant activities and low cytotoxicity. We propose that the Virola oleifera-capped AuNPs have potential biomedical applications.

Interaction energy profile for diphenyl diselenide in complex with δ-aminolevulinic acid dehydratase enzyme using quantum calculations and a molecular fragmentation method

Studies has pointed out the selenocompound diphenyl diselenide [(PhSe)2] as a novel promising drug with antioxidant, neuroprotective, anti-atherosclerotic and anti-inflammatory effects. In the opposite way, (PhSe)2 can also present cytotoxic properties and inhibit the activity of δ-aminolevulinic acid dehydratase (δALAD) and other thiol-containing proteins. δALAD inhibition can impair heme biosynthesis and, consequently, affect the aerobic metabolism. In order to deepen the analysis of the molecular mechanisms concerning δALAD inhibition by (PhSe)2, we performed theoretical quantum calculations within the Density Functional Theory (DFT) approach related to the interaction energies between amino acid residues and (PhSe)2 via Molecular Fragmentation with Conjugated Caps (MFCC) method. The quantum calculations revealed that interactions between (PhSe)2 moieties and δALAD could occur up to 9 Å distance from the (PhSe)2 active site centroid located inside the TIM barrel active site of δALAD. In addition, Phe208, Phe79, Cys122, Cys124, Pro125, Asp120, Lys199, Lys252, and Cys132 presented stronger attractive interaction energies to (PhSe)2 than to other closer residues and could be pointed out as essential for complex stability (interaction energy values ranging from −23.75 kcal·mol−1 to −11.74 kcal·mol−1 for DFT LDA/PWC and from −19.75 kcal·mol−1 to −6.76 kcal·mol−1 for DFT GGA/PW91). The analysis of the calculated energy values and the electrostatic potential together clarify that the two phenyl moieties in (PhSe)2 are key players in strongly attracting to aromatic, hydrophobic, and positively charged side chains from residues of the δALAD active site. Consequently, the spatial orientation assumed by (PhSe)2 allows the electrophile moiety Se-Se closer to thiolate groups of catalytic Cys122, Cys124, and Cys132, leading to consequent thiol oxidation and zinc release. In conclusion, these pieces of information may improve the previous understanding of the molecular docking model and could be useful to guide future studies concerning the rational design of novel diselenide-derived drugs with low affinity for δALAD.

A Force Balanced Fragmentation Method for ab Initio Molecular Dynamic Simulation of Protein.

A force balanced generalized molecular fractionation with conjugate caps (FB-GMFCC) method is proposed for ab initio molecular dynamic simulation of proteins. In this approach, the energy of the protein is computed by a linear combination of the QM energies of individual residues and molecular fragments that account for the two-body interaction of hydrogen bond between backbone peptides. The atomic forces on the caped H atoms were corrected to conserve the total force of the protein. Using this approach, ab initio molecular dynamic simulation of an Ace-(ALA)9-NME linear peptide showed the conservation of the total energy of the system throughout the simulation. Further a more robust 110 ps ab initio molecular dynamic simulation was performed for a protein with 56 residues and 862 atoms in explicit water. Compared with the classical force field, the ab initio molecular dynamic simulations gave better description of the geometry of peptide bonds. Although further development is still needed, the current approach is highly efficient, trivially parallel, and can be applied to ab initio molecular dynamic simulation study of large proteins.

Fragment-based quantum mechanical calculation of protein-protein binding affinities.

The electrostatically embedded generalized molecular fractionation with conjugate caps (EE-GMFCC) method has been successfully utilized for efficient linear-scaling quantum mechanical (QM) calculation of protein energies. In this work, we applied the EE-GMFCC method for calculation of binding affinity of Endonuclease colicin-immunity protein complex. The binding free energy changes between the wild-type and mutants of the complex calculated by EE-GMFCC are in good agreement with experimental results. The correlation coefficient (R) between the predicted binding energy changes and experimental values is 0.906 at the B3LYP/6-31G*-D level, based on the snapshot whose binding affinity is closest to the average result from the molecular mechanics/Poisson-Boltzmann surface area (MM/PBSA) calculation. The inclusion of the QM effects is important for accurate prediction of protein-protein binding affinities. Moreover, the self-consistent calculation of PB solvation energy is required for accurate calculations of protein-protein binding free energies. This study demonstrates that the EE-GMFCC method is capable of providing reliable prediction of relative binding affinities for protein-protein complexes. © 2018 Wiley Periodicals, Inc.

Prostate Cancer Screening Perception, Beliefs, and Practices Among Men in Bamenda, Cameroon.

Prostate Cancer (CaP) is the most commonly diagnosed cancer among Cameroonian men. Due to inadequate infrastructure, record keeping, and resources, little is known about its true burden on the population. There are rural/urban disparities with regards to awareness, screening, treatment, and survivorship. Furthermore, use of traditional medicine and homeopathic remedies is widespread, and some men delay seeking conventional medical treatment until advanced stages of CaP. This study examined the perceptions, beliefs, and practices of men in Cameroon regarding late stage CaP diagnoses; identified factors that influence screening decision; and ascertained how men decided between traditional or conventional medicine for CaP diagnosis and treatment.Semistructured focus groups were used to collect data from men in Bamenda, Cameroon. Qualitative data analysis was used to analyze transcripts for emerging themes and constructs using a socio-ecological framework.Twenty-five men participated in the study, with an average age of 59. Most of the participants had never received a prostate screening recommendation. Socioeconomic status, local beliefs, knowledge levels, awareness of CaP and screening methods, and stigma were prominent themes.A significant number of Cameroonian men receive late stage CaP diagnosis due to lack of awareness, attitudes, cultural beliefs, self-medication, and economic limitation. To effectively address these contributing factors to late stage CaP diagnosis, a contextually based health education program is warranted and should be tailored to fill knowledge gaps about the disease, dispel misconceptions, and focus on reducing barriers to utilization of health services.

Single-crystal perovskite CH3NH3PbBr3 prepared by cast capping method for light-emitting diodes

In this study, electroluminescence from single crystals of CH3NH3PbBr3 perovskite is explored. The cast capping method was applied to fabricate simple devices with an ITO/CH3NH3PbBr3/ITO structure. The devices showed a low operation voltage of 2 V and a pure green luminescence with full width at half maximum of ∼20 nm. However, the emission occurring at the crystal edges demonstrated blinking with a subsecond time interval, which is similar to the previously reported photoluminescence behavior of nanocrystal perovskites. This electroluminescence blinking may provide new insight into the recombination processes depending on the carrier traps and defects of emission layers in perovskite light-emitting devices.

Fine relocation, mechanism, and tectonic indications of middle-small earthquakes in the Central Tibetan Plateau

The medium-small earthquakes that occurred in the middle part of Tibetan Plateau (32°N–36°N, 90°E–93°E) from August 2016 to June 2017 were relocated using the absolute earthquake location method Hypo2000. Compared to the reports of Chinese Seismological Networks, our relocation results are more clustered on the whole, the horizontal location differences exceed 10 km, and the focal depths are concentrated in 0–8 km, which indicates that the upper crust inside the Tibetan Plateau is tectonically active. In June 2017 altogether eight earthquakes above magnitude 3.0 took place; their relocated epicenters are concentrated around Geladaindong. The relocation results of M<3.0 small earthquakes also showed obvious differences. Therefore, we used the CAP method to invert for the focal mechanisms of theM ≥3.0 earthquakes; results generally tally with the surface geological structures, indicating that the Tibetan Plateau is still under the strong compressional force from the India Plate. Among them the eight earthquakes that occurred near Geladaindong in June 2017 are all of normal fault type or with some strike-slip at the same time; based on previous research results we conjecture that these events are intense shallow crust responses to deep crust-mantle activities.

Comparative Study of Dimensional Accuracy in Three Dental Implant Impression Techniques: Open Tray, Closed Tray with Impression Coping, and Snap Cap

Several impression techniques have been proposed to result passive fitness between the prosthesis and osseointe-grated implant. The aim of the study was to compare dimensional accuracy of three impression methods: Open tray, closed tray with impression coping, and closed tray with snap cap. In this experimental study, a mandibular acrylic model was prepared with a milling machine to place three holes for dental implant analogs (Dio SM) with the dimension of 3.8 × 10 mm into the intended sites (one in midline and two others on the side at a distance of 10 mm) parallel with each other and perpendicular to the plane. Twenty-seven casts were prepared with impression material of polyvinyl siloxane (PVS) and dental stone type IV and divided into three groups. Implant situations were measured by coordinate measuring machine (CMM) and results were analyzed with Kruskal-Wallis and Mann-Whitney test to perform pairwise comparison among the groups. The mean ΔR values for open tray, closed tray with impression coping, and closed tray with snap cap were respectively, 0.070 ± 0.088, 0.173 ± 0.205, and 0.142 ± 0.044. There were statistically significant differences between open tray and closed tray as well as open tray and snap cap methods (p < 0.05), but there was no statistically significant difference between closed tray and snap cap method (p = 0.1). Regarding the results, open tray impression technique had the highest dimensional accuracy compared with the other two methods. There were no statically significant differences between closed tray with snap cap and closed tray with impression coping technique. Snap cap technique is less time consuming with similar dimensional accuracy in comparison with open tray impression technique.

Preço de transferência e seus impactos contábeis e fiscais dentro de uma empresa de filtros automobilísticos na importação e exportação de mercadorias

A legislação brasileira exige lançamentos contábeis específicos, quando o assunto é Preço de Transferência. Essas regras existentes foram criadas para evitar que as empresas brasileiras com subsidiárias no exterior possam utilizar a estratégia de evasão de divisas, já que sem ordenamento jurídico adequado os preços poderiam ser subavaliados para que não houvesse o devido pagamento dos tributos, na transferência de produtos ao exterior. O objetivo deste estudo consiste em verificar os impactos contábeis e fiscais no uso do preço de transferência na importação e exportação de mercadorias, para uma empresa do ramo automobilístico. Para tanto, utilizou-se a pesquisa aplicada, por meio da coleta de dados documentais e entrevista não estruturada. Considerando as penalidades legais quando a legislação não é aplicada corretamente, apresentou-se o seguinte problema de pesquisa: Quais os impactos contábeis e fiscais, quando aplicados as formas de cálculo adequadas ao preço de transferência? Os resultados obtidos para o cálculo da importação para o produto P603 mostraram que o método PRL Revenda, por obter o menor ajuste comparado ao método PIC no ano de 2014, foi o mais adequado a ser utilizado no cálculo do preço de transferência. No momento da exportação o método CAP foi o mais adequado contábil e fiscalmente, para os produtos F175F13 e R161F042, por ser o único método possível para calcular o preço de transferência para a empresa estudada. Como conclusão da pesquisa, verificou-se que a utilização dos métodos recomendados pela legislação fiscal vigente no Brasil poderiam contribuir para a qualidade da informação contábil e, ao mesmo tempo, resultariam num aumento da base de cálculo dos tributos incidentes sobre a receita.

Impact of contact integrity during thermal stress testing on degradation analysis of copper-plated silicon solar cells

In this study, silicon solar cells with copper-plated front side metallisation were exposed to long-term reliability thermal stress conditions and the material integrity of the plated contacts after stress testing was investigated using imaging and electrical measurements. Significant voltage ‘bend-back’ was observed in Suns-VOC measurements at high illumination intensities (> 1Sun) following thermal stress testing at 200°C for 500h of laser-ablated cells with a nickel/copper/silver plated front metal grid. Using a combination of focussed ion beam milling, high resolution imaging and energy dispersive X-ray spectroscopy, it was shown that large voids can form between the silver capping layer and the main copper stack during thermal annealing. However, even more revealing was the detection of a new metal layer comprising largely of diffused copper overlying the silver capping. The cause of the Schottky ‘bend-back’ behaviour was theorised to be due to increased contact resistance arising from the voids which are presumed to form as a result of grain boundary diffusion of copper through the silver capping layer. Errors of 5–10% in the determination of pFF from Suns-VOC occur as a result, with the scale of the error dependent on the capping method and sintering conditions. Collapsing the voids was subsequently shown to remove the Schottky behaviour and improve reliability of the fitted diode parameters extracted from Suns-VOC measurements.