PV Structures Research Articles

Characterization of isolates that cause black rot of crucifers in East Africa

A study was conducted in the East African countries of Kenya, Tanzania and Uganda in the months of July and August 2009 with the objectives of assessing the status of black rot and race structure of Xanthomonas campestris pv. campestris in the three countries. Samples infected with black rot were collected from farmers’ fields mainly from Brassica oleracea crops (broccoli, cabbage, cauliflower and kales). A total of 399 farms were surveyed of which 260 were from Kenya, 91 from Tanzania and 48 from Uganda. Following successful isolations, a total of 249 isolates of the causal agent, Xanthomonas campestris pv. campestris were recovered. Pathogenicity of all isolates was confirmed on B. oleracea susceptible cultivars Copenhagen Market F1 and Wirosa F1. Sixty of the 250 isolates were race-typed using a differential set Brassica spp. Only two races, 1 (Kenya and Tanzania) and 4 (Kenya, Tanzania and Uganda) were observed however, another race (5) was observed from one isolate recovered from a B. rapa sample obtained from Tanzania in 2003. Genomic fingerprinting with repetitive-PCR revealed clusters that did not depict significant correlations between isolates and geographical location, isolates and host adaptation or isolates and race. However, it did demonstrate existence of genetic differences within the East African X. campestris pv. campestris population indicating that it is not a similar clonal population of the same genetic background.

High-Vacuum Evaporation of n-CuIn3Se5 Photoabsorber Films for Hybrid PV Structures

Thin films of Cu-In-Se (CISe) photoabsorber with an overall composition of CuIn3Se5 were deposited onto glass/indium tin oxide (ITO) substrates from a polycrystalline bulk CuIn3Se5 source using the high-vacuum evaporation technique. Thermal conditions for the substrates during the evaporation process and the subsequent annealing in vacuum were selected to prepare polycrystalline n-CuIn3Se5 photoabsorber layers for use in hybrid photovoltaic structures based on an inorganic photoabsorber and conductive polymer functional layers. The CISe layers were deposited at a substrate temperature of 200°C and were annealed at temperatures from 300°C to 500°C in vacuum. Part of the as-deposited CISe was annealed twice, in argon and in vacuum at 500°C. These layers exhibited high photosensitivity and photoconductivity when illuminated with white light at an intensity of 100 mW/cm2. The results showed that the chalcopyrite structure of the prepared CISe photoabsorber films adhered well to the glass/ITO substrate. The average value of charge carrier concentration and the profile of charge carrier concentration in the annealed CISe photoabsorber layer were calculated using impedance spectroscopy.

Intriguing sequence of GaFeO3structures and electronic states to 70 GPa

Structural studies of the ferrimagnetic (${T}_{\mathrm{N}}$ = 200 K) Mott insulator GaFeO${}_{3}$ (SG Pc2${}_{1}n$) to 70 GPa, complemented by ${}^{57}$Fe M\"ossbauer spectroscopy and resistance (R) measurements at compression, decompression, and recompression, reveal a fascinating sequence of structures. Starting at \ensuremath{\sim}25 GPa a new structure, an orthorhombic perovskite (Pv) (SG Pbnm), is sluggishly formed followed by a volume V(P) drop of 5.4%. The complete formation of the Pv occurs at 42 GPa. In the 0--33 GPa range ${T}_{\mathrm{N}}$ reaches 300 K and R(P) decreases by one order of magnitude. At 53 GPa an isostructural transition is detected, characterized by a discontinuous drop of V(P) by \ensuremath{\sim}3%. M\"ossbauer spectra (MS) reveal a nonmagnetic component coexisting with the magnetic one at \ensuremath{\sim}60 GPa. Its abundance increases and above 77 GPa no sign of a magnetic hyperfine interaction is detected down to 5 K. Concurrently, one observes a continuous yet precipitous decrease in R(P) taking place in the 53--68 GPa range, leading to an onset of the metallic state at P = 68 GPa. These electronic/magnetic features of the high pressure (HP) Pv are consistent with a Mott transition. With pressure decrease below 50 GPa, the insulating Pv is recovered, and at \ensuremath{\sim}24 GPa a 1st-order structural transition takes place to a LiNbO${}_{3}$-type structure with SG R3c. This structure remains stable down to ambient pressure and with recompression it is stable up to 50 GPa, afterwards it transforms back to the HP Pv structure. It is noteworthy that this transition occurs at the same pressure, regardless of the preceding structures: Pbnm or R3c. The results are compared with hematite (Fe${}_{2}$O${}_{3}$, SG $R\overline{3}c$) and other ferric oxides. The mechanisms of the transitions are discussed.

Conductive polymer PEDOT:PSS back contact for CdTe solar cell

Two types of superstrate glass/ITO/CdS/CdTe PV structures were prepared by high vacuum evaporation technique with (i) activation of CdS layer and CdS/CdTe bi-layer structure step-by-step and (ii) activation of CdS/CdTe bi-layer structure. The activation was performed by annealing the structures with CdCl 2 in air at 400 °C for 15 min. Main conditions for CdS and CdTe thin films deposition and following treatment were selected from the literature data with the purpose to prepare and compare complete CdTe solar cells with standard p + Cu x Te back contact and conductive polymer poly(3,4-ethylenedioxythiophene) doped with polystyrene sulfonic acid (PEDOT:PSS) back contact. Obtained layers and structures were characterized using the XRD, SEM and I-V methods. Both the methods of activation treatment give comparable results from the point of view PV properties of complete solar cells. It was found that highly conductive PEDOT:PSS intermediate layer can significantly improve the back contact characteristics of CdTe. However these hybrid structures need to be further optimized to compete successfully with conventional inorganic back contacts in complete CdTe solar cells.

GaN photovoltaic leakage current and correlation to grain size

GaN p-i-n solar PV structures grown by rf plasma assisted molecular beam epitaxy (MBE) produce high performance IV characteristics with a leakage current density of less than 1×10−4 mA cm−2 at 0.1 V forward bias and an on-resistance of 0.039 Ω cm2. Leakage current measurements taken for different size diodes processed on the same sample containing the solar cells reveal that current density increases with diode area, indicating that leakage is not a large function of surface leakage along the mesa. Nonannealed Pt/Au Ohmic p-contacts produce a contact resistivity of 4.91×10−4 Ω cm−2 for thin Mg doped contact layers with sheet resistivity of 62196 Ω/◻. Under concentrated sunlight the cells produce an open-circuit voltage of 2.5 V and short circuit currents as high as 30 mA cm−2. Multiple growths comprised the study and on each wafer the IV curves representing several diodes showed considerable variation in parasitic leakage current density at low voltages on some wafers and practically no variation on others. It appears that a smaller grain size within the GaN thin film accounts for higher levels of dark current.

Theoretical study of the performance of a novel PV/e roof module for heat pump operation

In this paper, a novel PV/e roof module was designed to act as the roof element, electricity generator and the evaporator of a heat pump system. The modules, in conjunction with a heat pump, are able to provide heat and power supply to buildings with an enhanced efficiency. Energy profiles of the PV/e modules and modules-based heat pump system were analysed and temperature distribution across the module layers was studied. It was found that the PV/e roof modules-based heat pump system can achieve significant improvement in thermal and electrical efficiencies. Variation of the system efficiencies (thermal, electrical and total) with a number of factors, i.e., top cover, PV cells, evaporation and condensation temperature of the heat pump was investigated, which led to suggestion of the optimised system configuration and operating conditions. The study indicated that the combined system should operate at 10 °C of evaporation and 60 °C of condensation temperature. Borosilicate as a top cover has better thermal performance than polycarbonate and glass; whilst the mono-crystalline photovoltaic cells are of higher electrical efficiency over the poly-crystalline and thin-films. Under a typical Nottingham (UK) operating condition, the modules would achieve 55% of thermal efficiency and 19% of electrical efficiency, while the module-based heat pump system would have an overall efficiency of above 70%. It was also addressed that the integration of the PV cells and evaporation coil into a prefabricated roof would lead to large saving in both capital and running costs over separate arrangements of PV, heat pump and roof structure.

Potential existence of post-perovskite nitrides; DFT studies of ThTaN 3

Within density functional theory, the equations of state for cubic perovskite (c- pv) and hypothetic orthorhombic perovskite (o- pv GdFeO 3-type) and post-perovskite ( ppv) forms of ThTaN 3 are obtained. The decreasing volume and stabilizing energy indicate pressure enabled transitions: c- pv →o- pv → ppv. From electronic structure analysis the chemical system is found insulating in the c- pv ground state form with ∼ 1 eV band gap and semi-conducting for the ppv due to increased covalence. The chemical bonding properties show that Th and Ta bondings with the 2 N sites are selectively differentiated and reinforced for Ta–N bond within ppv form. This is the consequence of the corner as well as edge sharing octahedra characterizing ppv while pv structures have only corner sharing octahedra. It is the first case of potential post-perovskite nitride.

NLPCA as a diagnostic tool for control valve stiction

A significant number of control loops in process plants perform poorly due to control valve stiction. Developing a method to detect valve stiction in the early phase is imperative to avoid major disruptions to the plant operations. Nonlinear principal component analysis (NLPCA), widely known for its capability in unravelling nonlinear correlations in process data, is extended in this paper to diagnose control valve stiction problems. The present work is based on distinguishing the difference between the shapes of the signals caused by stiction and other sources, and utilizes the operating data of controlled variable-controller output ( pv– op). The structure of pv– op data used in this work is of sufficiently low dimension such that the NLPCA’s output allows the usage of simple mathematical tests in quantifying the nonlinear behavior of the loop. It is shown that if the underlying structure of pv– op data is linear, the NLPCA output generally approximates to a straight line with a regression coefficient ( R 2) greater than 0.8, otherwise there is a possibility of presence of nonlinearity or non-Gaussianity. The presence of stiction is then detected via a new and simple NLPCA curvature index, I NC . Results from simulated and real industrial case studies show that NLPCA is a very promising tool for detecting valve stiction.

Chemically Deposited Silver Antimony Selenide Thin Films for Photovoltaic Applications

AbstractSilver antimony selenide (AgSbSe2) thin films were prepared by heating sequentially deposited antimony sulphide (Sb2S3), silver selenide (Ag2Se) and Ag thin films in close contact with a selenium thin film. Sb2S3 thin film was prepared from chemical bath containing SbCl3 and Na2S2O3, Ag2Se from the bath containing AgNO3 and Na2SeSO3 and Se thin films from an acidified solution of Na2SeSO3, at room temperature on cleaned glass substrates. Ag thin film was deposited by vacuum thermal evaporation. The annealing temperature was varied from 300-390°C in vacuum (∼10−3 Torr) for 1 h. X-ray diffraction analysis showed the films formed at 350 °C was polycrystalline AgSb(S,Se)2 or AgSbSe2 depending on selenium thin film thickness. Morphology of these films was analyzed using Atomic Force Microscopy and Scanning Electron Microscopy. The elemental analysis was done using Energy Dispersive X-ray technique. Optical characterization of the thin films was done by optical transmittance spectra. The electrical characterizations were done using Hall effect and photocurrent measurements. A photovoltaic structure: Glass/ITO/CdS/AgSbSe2/Ag was formed, in which CdS was deposited by chemical bath deposition. J-V characteristics of this PV structure showed Voc=370 mV and Jsc=0.5 mA/cm2 under illumination using a tungsten halogen lamp.

Synthesis, characterization, reactivity and antibacterial activity of new peroxovanadium(V) complexes anchored to soluble polymers

New peroxovanadate (pV) complexes anchored to soluble polymers of the type, Na 3[V 2O 2(O 2) 4(carboxylate)]–PA [PA = poly(acrylate)] (PAV) and Na 2[VO(O 2) 2(carboxylate)]–PMA [PMA = Poly(methacrylate)] (PMAV) have been synthesized from the reaction of V 2O 5 with H 2O 2 and the sodium salts of the respective macromolecular ligands at pH ca. 6. The compounds were characterized by elemental analysis, SEM, EDX, TGA and spectral studies. In PMAV, the pV moieties are anchored in monomeric form to the polymer chain through unidentately co-ordinated O (carboxylate) atoms. Carboxylate groups of PA chain co-ordinate to V(V) centres, in a bridging bidentate fashion leading to the formation of dimeric pV structures in PAV. The PAV complex efficiently mediated bromination of organic substrates in aqueous-organic media at ambient temperature. Complex PMAV, was inactive in bromination under analogous conditions. The compounds are relatively resistant to degradation by the enzyme catalase compared to its natural substrate, H 2O 2. The polymeric complexes along with the free polymer and neat DPV were screened for their antibacterial activity against Staphylococcus aureus and Escherichia coli.

Texture development and TEM analysis of deformed CaIrO3: Implications for the D″ layer at the core‐mantle boundary

CaIrO3 is an isostructural analog for MgSiO3 post‐perovskite (ppv), likely the dominant mineral phase in the D″ layer. At high temperature CaIrO3 undergoes a phase transition to a perovskite (pv) structure. We have performed deformation experiments of CaIrO3 pv and ppv with the deformation‐DIA apparatus. The deformed pv does not display any discernable texture even after strong coaxial shortening. In contrast, ppv displays a strong lattice preferred orientation (LPO) with the a‐axis parallel to the shear direction and the b‐axis perpendicular to the shear plane. Calculation of the seismic properties predicts a shear wave splitting with a maximum of 2.7% in the shear plane, which is qualitatively compatible with seismic measurements. Ppv displayed a high density of (010)[100] dislocations, consistent with the textural results. Thus, our experiments on CaIrO3 pv and ppv are compatible with a seismically isotropic lower mantle and anisotropic D″ layer in the Earth.

Electrodeposited (Cu–In–Se)/polypyrrole PV structures

Hybrid PV structures based on polycrystalline photoabsorber Cu–In–Se (CISe) and electrically conductive polymer polypyrrole (PPy) were prepared using the electrodeposition technique. The PPy is considered as p-type barrier layer on n-CISe in the cell structure. Photoactive CISe thin films of various compositions were deposited electrochemically onto glass/ITO substrates from aqueous solutions containing CuSO 4, In 2(SO 4) 3 and SeO 2. All the obtained polycrystalline CISe films were annealed in vacuum to improve the crystalline structure and etched in 10% KCN to remove the additional phases. In order to prepare the PV structures, thin PPy films doped with β-naphthalene sodium sulfonate were galvanostatically electrodeposited onto the CISe films. Appropriate parameters of electrodeposition were selected experimentally. The morphology and thickness of the prepared film layers were determined using the SEM technique. The chemical composition of the CISe films was determined by energy dispersive X-ray spectroscopy (EDS). To investigate the electrical properties of the obtained structures, current–voltage and impedance characteristics were measured. The best structure showed an open-circuit voltage of 138 mV and a short-circuit current density of 2.55 mA/cm 2 under white light illumination with an intensity of 100 mW/cm 2.

Energy payback and life‐cycle CO2 emissions of the BOS in an optimized 3·5 MW PV installation

AbstractThis study is a life‐cycle analysis of the balance of system (BOS) components of the 3·5 MWp multi‐crystalline PV installation at Tucson Electric Power's (TEP) Springerville, AZ field PV plant. TEP instituted an innovative PV installation program guided by design optimization and cost minimization. The advanced design of the PV structure incorporated the weight of the PV modules as an element of support design, thereby eliminating the need for concrete foundations. The estimate of the life‐cycle energy requirements embodied in the BOS is 542 MJ/m2, a 71% reduction from those of an older central plant; the corresponding life‐cycle greenhouse gas emissions are 29 kg CO2 eq./m2. From field measurements, the energy payback time (EPT) of the BOS is 0·21 years for the actual location of this plant, and 0·37 years for average US insolation/temperature conditions. This is a great improvement from the EPT of about 1·3 years, estimated for an older central plant. The total cost of the balance of system components was $940 US per kWp of installed PV, another milestone in improvement. These results were verified with data from different databases and further tested with sensitivity‐ and data‐uncertainty analyses. Copyright © 2005 John Wiley & Sons, Ltd.

Theoretical possibilities of InxGa1−xN tandem PV structures

We designed a model of In x Ga 1− x N tandem structure made of N successive p–n junctions going from two junctions for the less sophisticated structure to six junctions for the most sophisticated. We simulated the photocurrent density and the open-circuit voltage of each structure under AM 1.5 illumination in goal to optimize the number of successive junctions forming one structure. For each value of N, we assumed that each junction absorbs the photons that are not absorbed by the preceding one. From the repartition of photons in the solar spectrum and starting from the energy gap of GaN, we fixed the gap of each junction that gives the same amount of photocurrent density in the structure. Then we calculated the current density accurately and optimized the thicknesses of p and n layers of each junction to make it give the same output current density. The evaluation of n i : the intrinsic concentration permitted to calculate the saturation current density and the open-circuit voltage of each junction. Assuming an overall fill factor of 80%, we divided the output peak power by the incident solar power and obtained the efficiency of each structure. The numerical values for In x Ga 1− x N were taken from the relevant literature. The calculated efficiency goes from 27.49% for the two-junction tandem structure to 40.35% for a six-junction structure. The six-junction In x Ga 1− x N tandem structure has an open-circuit voltage of about 5.34 V and a short circuit current density of 9.1 mA/cm 2 .

Analysis of the cloverleaf element in a human rhinovirus type 14/poliovirus chimera: correlation of subdomain D structure, ternary protein complex formation and virus replication.

RNA genomes of enteroviruses and rhinoviruses contain a 5'-terminal structure, the cloverleaf (CL), which serves as signal in RNA synthesis. Substitution of the poliovirus [PV1(M)] CL with that of human rhinovirus type 2 (HRV2) was shown previously to produce a viable chimeric PV, whereas substitution with the HRV14 CL produced a null phenotype. Fittingly, the HRV14 CL failed to form a complex with PV-specific proteins 3CD(pro)-3AB or 3CD(pro)-PCBP2, considered essential for RNA synthesis. It was reported previously (Rohll et al., J Virol 68, 4384-4391, 1994) that the major determinant for the null phenotype of a PV/HRV14 chimera resides in subdomain Id of the HRV14 CL. Using a chimeric PV/HRV14 CL in the context of the PV genome, stem-loop Id of HRV14 CL was genetically dissected. It contains the sequence C(57)UAU(60)-G, the underlined nucleotides forming the loop that is shorter by 1 nt when compared to the corresponding PV structure (UUGC(60)GG). Insertion of a G nucleotide to form a tetra loop (C(57)UAU(60)GG(61)) did not rescue replication of the chimera. However, an additional mutation at position 60 (C(57)UAC(60)GG(61)) yielded a replicating genome. Only the mutant PV/HRV14 CL with the UAC(60)G tetra loop formed ternary complexes efficiently with either PV proteins 3CD(pro)-3AB or 3CD(pro)-PCBP2. Thus, in the context of PV RNA synthesis, the presence of a tetra loop in subdomain D of the CL per se is not sufficient for function. The sequence and, consequently, the structure of the tetra loop plays an essential role. Biochemical assays demonstrated that the function of the CL element and the function of the cis-acting replication element in the 3D(pol)-3CD(pro)-dependent uridylylation of VPg are not linked.

O-specific polysaccharide structure of the aqueous lipopolysaccharide fraction from Xanthomonas campestris pv. vitians strain 1839

The structure of Xanthomonas campestris pv. vitians O-specific polysaccharide of the lipopolysaccharide fraction, extracted from the aqueous phase, was defined, on the basis of chemical and spectroscopical methods, as constituted by the following repeating unit: [ →3)- α- l - Rhap-(1 →] n3)- β- l - Rhap-(1 → where n is more frequently equal to 2, but it also assumes values equal to 1 and to 3.

Geographical Differentiation of the Population of Xanthomonas axonopodis pv. manihotis in Colombia

[This corrects the article on p. 4430 in vol. 63.].

Geographical Differentiation of the Population of Xanthomonas axonopodis pv. manihotis in Colombia

Analyses of DNA polymorphism and virulence variation were used to evaluate the population structure of Xanthomonas axonopodis pv. manihotis, the pathogen causing cassava bacterial blight in Colombia. We collected strains from the major cassava-growing regions which can be grouped into different edaphoclimatic zones (ECZs) according to environmental conditions, production constraints, and economic parameters. DNA polymorphism was assessed by a restriction fragment length polymorphism analysis, using an X. axonopodis pv. manihotis plasmid DNA sequence (pthB) as a probe to evaluate the genetic relatedness among 189 Colombian strains. The sampling intensity permitted the estimation of genetic differentiation within and among ECZs, sites, and fields and even within an individual plant. A multiple correspondence analysis indicated that the Colombian X. axonopodis pv. manihotis population showed a high degree of diversity relative to X. axonopodis pv. manihotis populations studied previously, and the entire collection was grouped into seven clusters. A general correlation was observed between the clusters and the geographical origin of the strains, as each cluster was largely composed of strains from the same ECZ. Representative strains, identified with pthB, were further characterized by ribotyping, hybridization to two repetitive genomic probes (pBS6 and pBS8), and restriction analysis of plasmid contents to evaluate the complementarity of these markers. Virulence variation was observed within the Colombian collection. Strains of different aggressiveness were found in all ecological zones, but no correlation between virulence variation and DNA polymorphism was observed. The genetic and virulence analyses contribute to understanding the X. axonopodis pv. manihotis population structure in Colombia.

Conformational Transmission in DNA

Abstract This poster presents our recent results on DNA dimers in which a stable trigonal bipyramidal pentacoordinated phosphorus (Pv) structure forms the internucleoside linkage. Conformational analysis of the systems 1-4 with 300 and 500 1H NMR has shown that the Pv structure results in a distorted conformation of the backbone structuE (1).

Shock wave equation of state of enstatite

Shock compression data are reported for hot‐pressed Bamble bronzite (En86) loaded to pressures between 104 and 161 GPa. When compared to earlier shock wave data on En90 at lower pressures and to static compression data, our data require the presence of a phase change. In P‐ρ space the data yield two distinct trajectories, which cannot be explained by experimental error. The higher‐density data, corrected for porosity and a small amount of metallic iron impurity, agree with a theoretical En86 high‐pressure phase Hugoniot calculated from static compression equation of state data for perovskite (pv) structure silicates when experimental errors and uncertainties in the equation of state parameters are considered. All the En86 data can be described by a calculated Hugoniot if the first pressure derivative of the MgSiO3 (pv) bulk modulus is taken as 4.5 ± 1.0. Combining the present preferred data with recent shock wave data for single‐crystal forsterite, we find that En86 is slightly more dense than Fo86 at pressures above 110 GPa. Comparison of the forsterite and enstatite data with the Preliminary Reference Earth Model (PREM) lower mantle densities, with corrections applied for the higher shock temperatures relative to lower mantle temperatures, shows that PREM densities are satisfied by olivine or pyroxene stoichiometries with Mg mole fractions from 0.82 to 0.90. These values are lower than estimates of 0.90 to 0.95 developed from extrapolating static compression data to lower mantle conditions.