Time-Dependent Error-Detection Rate Model for Software Reliability and Other Performance Measures

This paper presents a stochastic model for the software failure phenomenon based on a nonhomogeneous Poisson process (NHPP). The failure process is analyzed to develop a suitable meanvalue function for the NHPP; expressions are given for several performance measures. Actual software failure data are analyzed and compared with a previous analysis.     

Gentle STEM: ADF imaging and EELS at low primary energies

Aberration correction of the scanning transmission electron microscope (STEM) has made it possible to reach probe sizes close to 1 Å at 60 keV, an operating energy that avoids direct knock-on damage in materials consisting of light atoms such as B, C, N and O. Although greatly reduced, some radiation damage is still present at this energy, and this limits the maximum usable electron dose. Elemental analysis by electron energy loss spectroscopy (EELS) is then usefully supplemented by annular dark field (ADF) imaging, for which the signal is larger. Because of its strong Z dependence, ADF allows the chemical identification of individual atoms, both heavy and light, and it can also record the atomic motion of individual heavy atoms in considerable detail. We illustrate these points by ADF images and EELS of nanotubes containing nanopods filled with single atoms of Er, and by ADF images of graphene with impurity atoms.     

Higher-order aberration corrector for an image-forming system in a transmission electron microscope

We developed a new electron optical system with three dodecapoles to compensate for spherical aberration and six-fold astigmatism, which generally remains in a two-hexapole type corrector. In this study, we applied the corrector for image-forming system in transmission electron microscope. Compensation for higher-order aberration was demonstrated through a diffractogram tableau using a triple three-fold astigmatism field system, which was then compared with a double hexapole field system. Using this electron optical system, six-fold astigmatism was measured to be less than 0.1 mm at an acceleration voltage of 60 kV, showing that the system successfully compensated for six-fold astigmatism.     

Determination of water-soluble vitamins using a colorimetric microbial viability assay based on the reduction of water-soluble tetrazolium salts

A method for the determination of water-soluble vitamins using a colorimetric microbial viability assay based on the reduction of the tetrazolium salt {2-(2-methoxy-4-nitrophenyl)-3-(4-nitrophenyl)-5-(2,4-disulfophenyl)-2H-tetrazolium, monosodium salt (WST-8)} via 2-methyl-1,4-napthoquinone (NQ) was developed. Measurement conditions were optimized for the microbiological determination of water-soluble vitamins, such as vitamin B₆, biotin, folic acid, niacin, and pantothenic acid, using microorganisms that have a water-soluble vitamin requirement. A linear relationship between absorbance and water-soluble vitamin concentration was obtained. The proposed method was applied to determine the concentration of vitamin B₆ in various foodstuffs. There was good agreement between vitamin B₆ concentrations determined after 24 h using the WST-8 colorimetric method and those obtained after 48 h using a conventional method. The results suggest that the WST-8 colorimetric assay is a useful method for the rapid determination of water-soluble vitamins in a 96-well microtiter plate.     

Chemical Growth of 1T‐TaS2 Monolayer and Thin Films: Robust Charge Density Wave Transitions and High Bolometric Responsivity

Ultrathin two‐dimensional (2D) charge density wave (CDW) materials, with sharp resistance change at the phase‐transition temperature, yet with ultrathin thickness, hold great potential for electrical device applications. However, chemical synthesis of high‐quality samples and observation of the CDW states down to the monolayer limit is still of great challenge. Chemical vapor deposition of 1T‐TaS₂ sheets on hexagonal boron nitride (h‐BN) with robust CDW states even down to the monolayer extreme is reported here. Further, based on the near commensurate CDW to incommensurate CDW phase transition with a high temperature coefficient of resistance (TCR), highly responsive room‐temperature bolometers are fabricated by suspending the as‐grown 1T‐TaS₂ sheets.     

Synthesis of Co-Doped MoS2 Monolayers with Enhanced Valley Splitting

Internal magnetic moments induced by magnetic dopants in MoS₂ monolayers are shown to serve as a new means to engineer valley Zeeman splitting (VZS). Specifically, successful synthesis of monolayer MoS₂ doped with the magnetic element Co is reported, and the magnitude of the valley splitting is engineered by manipulating the dopant concentration. Valley splittings of 3.9, 5.2, and 6.15 meV at 7 T in Co-doped MoS₂ with Co concentrations of 0.8%, 1.7%, and 2.5%, respectively, are achieved as revealed by polarization-resolved photoluminescence (PL) spectroscopy. Atomic-resolution electron microscopy studies clearly identify the magnetic sites of Co substitution in the MoS₂ lattice, forming two distinct types of configurations, namely isolated single dopants and tridopant clusters. Density functional theory (DFT) and model calculations reveal that the observed enhanced VZS arises from an internal magnetic field induced by the tridopant clusters, which couples to the spin, atomic orbital, and valley magnetic moment of carriers from the conduction and valence bands. The present study demonstrates a new method to control the valley pseudospin via magnetic dopants in layered semiconducting materials, paving the way toward magneto-optical and spintronic devices.     

Morphology Engineering in Monolayer MoS2‐WS2 Lateral Heterostructures

In recent years, heterostructures formed in transition metal dichalcogenides (TMDs) have attracted significant attention due to their unique physical properties beyond the individual components. Atomically thin TMD heterostructures, such as MoS₂‐WS₂, MoS₂‐MoSe₂, MoS₂‐WSe₂, and WSe₂‐WS₂, are synthesized so far via chemical vapor deposition (CVD) method. Engineering the morphology of domains including size and shape, however, still remains challenging. Here, a one‐step CVD strategy on the morphology engineering of MoS₂ and WS₂ domains within the monolayer MoS₂‐WS₂ lateral heterostructures through controlling the weight ratio of precursors, MoO₃ and WO₃, as well as tuning the reaction temperature is reported. Not only can the size ratio in terms of area between WS₂ and MoS₂ domains be easily controlled from less than 1 to more than 20, but also the overall heterostructure size can be tuned from several to hundreds of micrometers. Intriguingly, the quantum well structure, a WS₂ stripe embedded in the MoS₂ matrix, is also observed in the as‐synthesized heterostructures, offering opportunities to study quantum confinement effects and quantum well applications. This approach paves the way for the large‐scale fabrication of MoS₂‐WS₂ lateral heterostructures with controllable domain morphology, and shall be readily extended to morphology engineering of other TMD heterostructures.