Laser THz emission microscope as a novel tool for LSI failure analysis

We have proposed and developed a novel technique for a non-contact inspection of defective interconnections in an LSI chip using a laser terahertz emission microscope (LTEM). The LTEM measures the THz emission images of an LSI chip by scanning it with fs laser pulses. When a fs laser pulse irradiates a p–n junction in an LSI chip, transient photocurrent flows into interconnections resulting in the emission of the THz pulse into free space. We investigated the characteristics of the THz emissions from simple test element group samples which consist of p–n junctions connected to metal lines. It was found that the metallic lines connected to photo-excited p–n junctions worked as THz emission antennae which enhance the emission efficiency of THz pulses near their resonant frequencies corresponding to the line lengths. This result indicates that THz emission signals from p–n junctions in circuits strongly depend on the structure of the interconnections. We show the successful results on the inspection of defective interconnections in MOSFET devices and C7552 ISCAS’85 benchmark circuits using LTEM. By comparing the THz emission images between a normal circuit and a defective one, it is possible to identify the p–n junctions connected to the defective interconnections without electrical contacts.     

Numerical study on the spark ignition characteristics of a methane-air mixture using detailed chemical kinetics: Effect of equivalence ratio, electrode gap distance, and electrode radius on MIE, quenching distance, and ignition delay

The minimum ignition energy (MIE) is an important property for designing safety standards and understanding the ignition process of combustible mixtures. Even though the formation of flame kernels in quiescent methane-air mixtures has been simulated numerically, the ignition mechanism has never been satisfactorily explained. This study investigated the spark ignition of methane-air mixtures through a numerical analysis using detailed chemical kinetics consisting of 53 species and 325 elementary reactions while considering the heat loss to the electrode. The simulation was used to investigate the quenching distance and the effects on the MIE of the electrode size, electrode gap distance, ignition duration, and equivalence ratio. The effect of the equivalence ratio on the ignition delay time was also examined. The simulated results showed the same trend as previous experimental results.     

Targeted gene replacement at the URA3 locus of the basidiomycetous yeast Pseudozyma antarctica and its transformation using lithium acetate treatment

The basidiomycetous yeast Pseudozyma antarctica is a remarkable producer of industrially valuable enzymes and extracellular glycolipids. In this study, we developed a method for targeted gene replacement in P. antarctica. In addition, transformation conditions were optimized using lithium acetate, single‐stranded carrier DNA and polyethylene glycol (lithium acetate treatment), generally used for ascomycetous yeast transformation. In the rice‐derived P. antarctica strain GB‐4(0), PaURA3, a homologue of the Saccharomyces cerevisiae orotidine‐5′‐phosphate decarboxylase gene (URA3), was selected as the target locus. A disruption cassette was constructed by linking the nouseothricine resistance gene (natMX4) to homologous DNA fragments of PaURA3, then electroporated into the strain GB‐4(0). We obtained strain PGB015 as one of the PaURA3 disruptants (Paura3Δ::natMX4). Then the PCR‐amplified PaURA3 fragment was introduced into PGB015, and growth of transformant colonies but not background colonies was observed on selective media lacking uracil. The complementation of uracil‐auxotrophy in PGB015 by introduction of PaURA3 was also performed using lithium acetate treatment, which resulted in a transformation efficiency of 985 CFU/6.8 μg DNA and a gene‐targeting ratio of two among 30 transformants. Copyright © 2017 John Wiley & Sons, Ltd.     

Improved cell viability of linear polyethylenimine through gamma-cyclodextrin inclusion for effective gene delivery

A polypseudorotaxane consisting of a linear polyethylenimine with Mn of 22,000 (LPEI22k) and gamma-cyclodextrins (gamma-CDs; LPEI22k/gamma-CD) has been examined as a gene carrier. The polyplex formation with luciferase-encoding plasmid DNA (pDNA), intracellular trafficking of polyplex, cytotoxicity, and transfection efficiency were evaluated by various characteristic methods. LPEI22k/gamma-CD formed a pDNA polyplex at higher N/P ratios than LPEI22k; this suggests that the gamma-CD threading sterically interfered with the polyplex formation. In addition, the zeta potentials of the polyplex significantly decreased due to the reduction in charge density of LPEI22k caused by gamma-CD threading. The cellular uptake of pDNA in the LPEI22k/gamma-CD polyplex was enhanced by free gamma-CDs released from the polyplex that might accelerate the cellular uptake through enhanced membrane affinity. LPEI22k/gamma-CD significantly increased cell viability even at high N/P ratios, and the polyplex showed high transfection efficacy. The low cytotoxicity and high gene expression of LPEI22k/gamma-CD are advantageous to polyplex administration in vivo.     

Occurrence of polybrominated biphenyls, polybrominated dibenzo-p-dioxins, and polybrominated dibenzofurans as impurities in commercial polybrominated diphenyl ether mixtures

The objective of this study was to determine the concentrations and compositions of polybrominated biphenyls (PBBs), polybrominated dibenzo-p-dioxins (PBDDs), and polybrominated dibenzofurans (PBDFs) as contaminants in the commercial polybrominated diphenyl ether (PBDE) mixtures DE-71, DE-79, and DE-83 and to ascertain the lot-to-lot variations in the proportions of these contaminants. Commercial PBDE mixtures tested in the present study contained both PBBs and PBDFs, as impurities, at concentrations in the range of several tens to several thousands of nanograms per gram. Concentrations of total PBDFs were greater than those of total PBBs in DE-79 and DE-83 mixtures. PBDDs were not detected at levels above the limit of detection. Profiles of PBB and PBDF congeners varied with the degree of bromination of the commercial PBDE mixtures (i.e., more highly brominated mixtures of PBDEs contained heavily brominated homologues of PBBs and PBDFs). On the basis of the production/ usage of commercial PBDE mixtures in 2001, potential global annual emissions of PBBs and PBDFs were calculated to be 40 and 2300 kg, respectively. Results of our study suggestthat PBDFs can also be formed during the production of commercial PBDE mixtures, in addition to their formation during pyrolysis of brominated flame retardants.     

Construction of an additional metal-binding site in human metallothionein-2

We have constructed a new metal-binding site in the human metallothionein-2 (hMT-2), using the protein as a scaffold to investigate the structure and function of metal-binding. Potential metal-binding sites were designed within hMT-2 on the basis of structures generated by homology modeling. Amino acid residues D11, C13, C26 and S28 in the beta-domain of hMT-2 (hMT-2beta) were found, by computer search, to form a potential tetrahedral Cys4 metal-binding site. Six mutant proteins were constructed with the following amino acid substitutions: D11C, S28C and D11C/S28C in hMT-2 and the same mutations in hMT-2beta, respectively. These single-mutant and double-mutant proteins bound one gram atom of cadmium or zinc ions per gram molecule of protein more than the corresponding wild-type proteins. The circular dichroism spectra suggested that the structures of the single-mutant proteins that bound Cd or Zn were similar to that of the D11C/S28C double-mutant proteins. To evaluate the metal-binding affinity of the mutant proteins, we performed pH titrations of wild-type and mutant proteins. The stability with changes in pH of all the mutant proteins was higher than that of the wild-type proteins, and that of the double-mutant D11C/S28C protein was highest. Consequently, it appears that we were able to create novel proteins that bound metal ions at high density and with high affinity.     

Effect of cellulose fibers addition on the mechanical properties and water vapor barrier of starch-based films

Starch-based films have promising application on food packaging, because of their environmental appeal, low cost, flexibility and transparency. Nevertheless, their mechanical and moisture barrier properties should be improved. The aim of this work was to enhance these properties by reinforcing the films with cellulose fibers. Besides, the influences of both the solubility coefficient of water in the films (β) and the diffusion coefficient of water vapor through the films (D^w) on the films' water vapor permeability (K^w) were investigated. Films were prepared by the so-called casting technique, from film-forming suspensions of cassava starch, cellulose fibers (1.2 mm long and 0.1 mm of diameter), glycerol and water. The influence of fibers addition on K^w was determined at three relative humidity gradient ranges, ΔRH (2–33%, 33–64% and 64–90%). Films reinforced with cellulose fibers showed higher tensile strength and lower deformation capacity, and presented lower K^w than films without fibers. K^w showed strong dependency of β and D^w, presenting values up to 2–3 times greater at ΔRH = 64–90% than at ΔRH = 33–64%, depending on the film formulation. Therefore, adding cellulose fibers to starch-based films is a viable alternative to improve their mechanical and water barrier properties. Besides, this work showed the importance of determining film's water vapor permeability simulating the real environmental conditions the film will be used.     

Constraint loss correction for assessment of CTOD fracture toughness under welding residual stress. Part I: Methodology using the equivalent CTOD ratio

This part I of a two-part paper presents a method of assessing the effects of welding residual stress and constraint loss on the cleavage fracture of a wide plate subjected to membrane stress based on the Weibull stress criterion. It has been found that the Weibull stress criterion is efficient for evaluating the fracture instability of wide plates with and without a welding residual stress field. The concept of an equivalent crack-tip opening displacement (CTOD) ratio β_r under a welding residual stress field is introduced for assessment of constraint loss effects on CTOD fracture toughness of wide plates. The equivalent CTOD ratio β_r is defined as the ratio of the CTOD in the standard fracture toughness specimen to the CTOD in a wide plate with a welding residual stress at the same level of the Weibull stress. Fracture assessment procedures using β_r for wide plates are shown within the framework of the failure assessment diagram. It has been found that the excessive conservatism observed in the conventional procedure can be reduced reasonably by applying the proposed method. The companion part II of the paper presents applications of the CTOD toughness correction method using β_r to the fracture test data of welded joints and verifies the proposed method in the ductile-brittle transition temperature region.     

A comparative study of different solvothermal methods for the synthesis of Sn<Superscript>2+</Superscript>-doped BaTiO<Subscript>3</Subscript> powders and their dielectric properties

Ternary oxides containing Sn²⁺ are rare and difficult to prepare by the conventional solid state reactions due to the disproportionation of Sn²⁺ to Sn⁴⁺ and Sn at high temperatures. In this article, Sn²⁺-doped barium titanate, Ba_1−x Sn _x TiO₃ (x = 0.00, 0.02, 0.05, and 0.10) nanopowders were successfully synthesized at a moderate temperature by a microwave-assisted solvothermal reaction (MSR) and a solvothermal reaction with rolling (SRR). The powders obtained using the MSR and SRR consisted of nanoparticles of 20–50 nm and 100–120 nm in diameter, respectively. The dielectric constant of the sample increased by doping with a small amount of Sn²⁺ (x ≤ 0.05), but decreased by doping in excess amounts of it.