Light trapping effect of submicron surface textures in crystalline Si solar cells

Recently, submicron textures have been researched and applied to multicrystalline silicon solar cells in order to improve their optical performance. In this study, the antireflection and light trapping effects of submicron surface textures in crystalline Si (c‐Si) solar cells were quantitatively investigated by numerical simulations based on Maxwell's equations with a simple two‐dimensional (2D) surface grating model. The calculated results showed that the surface reflection loss can be effectively reduced by using submicron Si surface gratings with appropriate aspect ratios. On the other hand, higher order diffractions that are caused by surface gratings that increase optical path lengths and light absorption near the band gap wavelength are dominant only for those with periods greater than 0·5 µm. From these results, it was inferred that submicron textures are effective for light trapping as well as for antireflection in thin c‐Si solar cells if appropriate dimensions are chosen. Copyright © 2007 John Wiley & Sons, Ltd.     

Determination of Critical Parameters Based on the Intensity of Transmitted Light Around Gas–Liquid Interface: Critical Parameters of CO_{2}

A precise determination of the critical temperature and density for technically important fluids would be possible on the basis of the digital image for the visual observation of the phase boundary in the vicinity of the critical point since the sensitivity and resolution are higher than those of naked eyes. In addition, the digital image can avoid the personal uncertainty of an observer. A strong density gradient occurs in a sample cell at the critical point due to gravity. It was carefully assessed to determine the critical density, where the density profile in the sample cell can be observed from the luminance profile of a digital image. The density-gradient profile becomes symmetric at the critical point. One of the best fluids, whose thermodynamic properties have been measured with the highest reliability among technically important fluids, would be carbon dioxide. In order to confirm the reliability of the proposed method, the critical temperature and density of carbon dioxide were determined using the digital image. The critical temperature and density values of carbon dioxide are ( \(304.143\,\pm \,0.005)\hbox { K}\) and ( \(467.7\,\pm \,0.6)\) kg \(\cdot \) m \(^{-3}\) , respectively. The critical temperature and density values agree with the existing best values within estimated uncertainties. The reliability of the method was confirmed. The critical pressure, 7.3795 MPa, corresponding to the determined critical temperature of 304.143 K is also proposed. A new set of parameters for the vapor-pressure equation is also provided.     

Electrical conductivities of M3P2O8 (M = Ca,Ba)

Two-probe conductivity measurements made for M₃P₂O₈ (M = Ca, Ba) suggested that the electrical conduction of these phosphates would primarily be due to the migration of Ca²⁺ and Ba²⁺ ions. At relatively low temperatures and high oxygen partial pressures, in contrast to Ca₃P₂O₈, however, Ba₃P₂O₈ shows partial electronic conduction.     

Generation of interstitial boron by minority-carrier injection

The performance of boron-doped CZ Si solar cell is degraded by the light irradiation and/or the minority carrier (electron) injection. To understand these phenomena, ab initio molecular orbital calculations are carried out using a cluster model. The theoretical results indicate that the activation energy for kicking out a substitutional B by the interstitial Si is decreased due to the injected electron. Therefore, the interstitial B is easily produced by the minority carrier injection and then diffuses in the Si crystal, resulting in the generation of the interstitial B and interstitial O defect complex.     

A study on the development of a multi-purpose spindle system for quality productive machining

A compact multi-purpose spindle for multi-tasking machine tools has been developed such that it can provide high power and torque for lower speed ranges while it rotates at high speeds for light duty machining. The innovative design based on the dual direct drive concept has been adopted such that the size of the spindle can stay the same as a conventional spindle of its class. For optimizing the design process, a method based on the complete virtual approach using 3D solid models has been studied and developed. Machining performance has been verified through a physical prototype.     

Thermostable glycerol kinase from a hyperthermophilic archaeon: gene cloning and characterization of the recombinant enzyme

The Pk-glpK gene, which encodes glycerol kinase (GK) from a hyperthermophilic archaeon Pyrococcus kodakaraensis KOD1, was cloned and expressed in Escherichia coli. The amino acid sequence of this enzyme (Pk-GK) deduced from the nucleotide sequence showed 57% identity with that of E. coli GK and 47% identity with that of human GK. Pk-GK, which has a molecular weight of 55902 (497 amino acid residues), was purified from E. coli and characterized. Despite the high sequence similarity, Pk-GK and E. coli GK are greatly divergent in structure and function from each other. Unlike E. coli GK, which exists as a tetramer, Pk-GK exists as a dimer. The preferred divalent cation for Pk- GK is Co2+, instead of Mg2+. The optimum pH and temperature for Pk-GK activity are 8.0 and 80 degrees C, respectively. Pk-GK can utilize other nucleoside triphosphates than ATP as a phosphoryl donor. It is fairly resistant to an allosteric inhibitor of E. coli GK, fructose-1,6- bisphosphate. Determination of the kinetic parameters indicates that the Km value of the enzyme is 15.4 microM for ATP and 111 microM for glycerol and its kcat value is 940 s(-1). The enzyme was shown to be fairly resistant to irreversible heat inactivation and still retained 50% of its enzymatic activity even after heating at 100 degrees C for 30 min. Construction of a model for the three-dimensional structure of the enzyme suggests that the formation of extensive ion-pair networks is responsible for the high stability of this enzyme.      

Hydrogen production by oxidative methanol reforming on Pd/ZnO: Catalyst preparation and supporting materials

Pd and Pd–Zn alloy were supported on various supporting materials using impregnation, co-precipitation and microemulsion methods, and their catalytic performances in oxidative methanol reforming (OMR) were investigated. Pd/ZnO exhibited much higher selectivity than either Pd/Al₂O₃ or Pd/ZrO₂ in the OMR for hydrogen production. This was attributed to the presence of Pd–Zn alloy on the ZnO support. Elemental Pd on Al₂O₃ or ZrO₂ promotes methanol decomposition reaction and increases CO formation. Using a microemulsion method, a highly selective Pd/ZnO can be obtained with much lower Pd loading than that in samples prepared by co-precipitation. Modification of Al₂O₃ with ZnO produced a ZnAl₂O₄ phase, which was found to be a good support for the Pd/ZnO catalyst. Highly active and selective Pd/ZnO/ZnAl₂O₄ catalysts for the OMR reaction, containing much lower Pd loadings have been developed by impregnation of the supports with an aqueous solution of Pd(NO₃)₂ + Zn(NO₃)₂.     

A comparative study of fracture behavior between carbon black/poly(ethylene terephthalate) and multiwalled carbon nanotube/poly(ethylene terephthalate) composite films

Fracture behavior of amorphous poly(ethylene terephthalate) (PET) films added multiwalled carbon nanotube (MWCNT) has been compared with that of the PET films added with carbon black (CB) to elucidate the effects of the large aspect ratio of MWCNT. Fracture toughness has been evaluated using the essential work of fracture tests. Evolution of the crazes has been analyzed by conducting time‐resolved small‐angle X‐ray scattering measurements during tensile deformation of the films at room temperature using synchrotron radiation. CB and MWCNT increased the fracture toughness of the PET film by increasing the plastic work of fracture. This resulted from the effects of the fillers to prevent the localization of deformation upon the crazes formed at earlier stages of tensile deformation and to retard the growth of the fibrils in the crazes to a critical length. The CB particles provided a number of sites where the crazes were preferably formed due to stress concentration. In the case of MWCNT, on the other hand, the widening of the crazes formed at earlier stages was suppressed due to the bridging effect arising from the large aspect ratio of MWCNT. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Analyses of homo-oligomer interfaces of proteins from the complementarity of molecular surface, electrostatic potential and hydrophobicity

To extract the general structural features of interacting protein pairs, the non-redundant homo-oligomer interfaces (393 interfaces) in the PDB were analyzed using the fine-grained molecular surface, electrostatic potentials and the hydrophobicity calculated as the solvation free energy using empirical parameters. For each property, statistical analyses of the degree of complementarity were carried out, and we developed a method to judge whether interfaces were shape-complementary, electrostatic-complementary and/or hydrophobic-complementary or not. In order to search for the correlation between the property complementarity and structure of the interfaces, at first, we roughly classified all the interfaces into the following five groups according to the structure of the interface and surveyed the correlation between the shape classification and the complementary: cyclic-oligomer (69), twisted-dimer (27), dimer-parallel (14), dimer-perpendicular (109) and dimer-circular (174), where the number in the parenthesis is the number of interfaces in each group. As a result, we found the new characteristic trends as the possible necessary conditions in the formation of homo-oligomer interfaces, especially from the viewpoint of electrostatic complementarity. In addition, we also show that complementarity analyses can be used to discriminate the biological-interface from the crystallographic-interface in homo-oligomer proteins.     

Fabrication of CdS/β-SiC/TiO2 tri-composites that exploit hole- and electron-transfer processes for photocatalytic hydrogen production under visible light

In this work, CdS/SiC/TiO₂ tri-composite photocatalysts that exploit electron- and hole-transfer processes were fabricated using an easy two-step method in the liquid phase. The photocatalyst with a 1:1:1 M ratio of CdS/SiC/TiO₂ exhibited a rate of hydrogen evolution from an aqueous solution of sodium sulfite and sodium sulfide under visible light of 137 μmol h^?1 g^?1, which is 9.5 times that of pure CdS. β-SiC can act as a sink for the photogenerated holes because the valence band level of β-SiC is higher than the corresponding bands in CdS and TiO₂. In addition, the level of the conduction band of TiO₂ is lower than those of CdS and β-SiC, so TiO₂ can act as the acceptor of the photogenerated electrons. Our results demonstrate that hole transfer and absorption in the visible light region lead to an effective hydrogen-production scheme.