Intramolecular C-H activation by inferred terminal cobalt imido intermediates

Reaction of TpR,MeCo(I) dinitrogen complexes (R = iPr, tBu) with trimethylsilyl azide yields structurally characterized compounds that imply the formation of reactive intermediates of the type TpR,MeCo=NSiMe3. These cobalt imido species apparently abstract hydrogen from the 3-substituent of the Tp-ligand, leading to the formation of amido complexes accompanied by either Co-C bond formation (R = tBu) or C-C bond formation (R = iPr).     

A novel homogeneous immunoassay for anthrax detection based on the AlphaLISA method: detection of B. anthracis spores and protective antigen (PA) in complex samples

Amplified Luminescent Proximity Homogeneous Assay (AlphaLISA) technology is an energy-transfer-based assay, utilizing singlet oxygen as an energy donor to a fluorescent acceptor. The long singlet oxygen migration distance allows the energy transfer mechanism to go up to ～200 nm, facilitating flexible and sensitive homogeneous immunoassays. While soluble protein detection using AlphaLISA was previously described, the detection of particles such as bacteria and viruses was not reported. In this work, we show for the first time the implementation of the AlphaLISA technology for the detection of a particulate antigen, i.e., Bacillus anthracis spores. Here, we show that an efficient particle immunoassay requires a high acceptor-to-donor ratio (>4:1). The results suggested that the high acceptor/donor ratio is required to avoid donor aggregation (“islands”) on the spore surface, hence facilitating donor/acceptor interaction. The developed assay enabled the detection of 10⁶ spores/mL spiked in PBS. We also demonstrate the development of a highly sensitive AlphaLISA assay for the detection of the main toxin component of anthrax, protective antigen (PA). The assay enabled the detection of 10 and 100 pg/mL PA in buffer and spiked naïve rabbit sera, respectively, and was successfully implemented in sera of anthrax-infected rabbits. To summarize, this study demonstrates that AlphaLISA enables detection of anthrax spores and toxin, utilizing short homogeneous assays. Moreover, it is shown for the first time that this technology facilitates the detection of particulate entities and might be suitable for the detection of other bacteria or viruses.     

Underquaternized anion exchange resins as covalent scavengers

The use of partially quaternized, chloromethylated polystyrene as a covalent scavenger of cholate ion in aqueous media has been demonstrated. The ability of such polymers to scavenge organic anions by covalent as well as by ionic means has important implications in the areas of medicinal and environmental chemistry, which are briefly discussed.     

Electrochromic cells with iridium oxide display electrodes

We report the fabrication and electrochromic behavior of iridium oxide film electrodes, including a specific display electrode design compatible with the high peak ion-insertion current densities accepted by this material and necessary for the shortest possible response time. The configuration of a complete two-terminal display cell, in which the high capacity counter electrode behaves as a pseudo-reference electrode, is presented. Cell performance, including the use of IR compensated constant-voltage address when response time is limited by impedances external to the iridium oxide itself, is reported.     

Three-species collisionless reconnection: effect of O+ on magnetotail reconnection

The nature of collisionless reconnection in a three-species plasma composed of a heavy species, protons, and electrons is examined. In addition to the usual two length scales present in two-species reconnection, there are two additional larger length scales in the system: one associated with a "heavy whistler" which produces a large scale quadrupolar out-of-plane magnetic field, and one associated with the "heavy Alfvén" wave which can slow the outflow speed and thus the reconnection rate. The consequences for reconnection with O+ present in the magnetotail are discussed.     

Ion debris mitigation from tin plasma using ambient gas,magnetic field and combined effects

Mitigation of energetic ions from laser produced tin plasma is one of the principal issues in the development of an extreme ultraviolet lithographic light source. We explored the possibility of using an ambient gas and/or a magnetic field for controlling the energetic ions from tin plasma. Hydrogen, helium and argon gases provide good transmission to 13.5 nm and are found to be an effective stopper for tin ions. Absorption of in-band radiation limits the density of gas below levels needed to completely protect optics. Tin ion ranges in buffer gases were estimated using the Monte Carlo simulation code SRIM and compared with experimental results. The presence of a moderate transverse magnetic field of 0.64 T slowed the propagation of fast moving tin ions but failed to stop them. The synergistic effect of a combination of magnetic field and an ambient gas is found to be very promising for mitigating tin ions without exceeding EUV gas absorption limits. PACS 42.72.Bj; 52.50.Jm; 52.55.Jd; 52.70.kz     

The critical velocity of mode-I fracture in a non-linear lattice in the absence of viscosity

The high-velocity regime of mode-I fracture is interesting, especially because of the instability of the steady-state propagating crack to a more complex dynamics (such as micro-branching). In this article, we study mode-I fracture in a non-linear lattice in the absence of a viscous force. In earlier study, we had studied the effects of the bond potential parameters, including Kelvin viscous force, on the macroscopic behavior of the crack, including the high velocity regime instability. Recently, a new study has appeared using a very similar non-linear force but claiming quite different results. In this article, we seek to discover an explanation of these differences. We find that they do not result from the viscosity present in our previous study. At least part of the differences are attributable, rather, to the very wide system used in the recent study, which leads to long transients and a failure to probe the steady-state behavior. Our results confirm our previously claimed lack of agreement with the Yoffe prediction for the critical velocity of a steady-state crack, and neither do they match the predictions of Gao’s model.     

Frequency offsets in frequency-locked semiconductor lasers

A commonly used technique for frequency locking a laser is dithering the laser frequency and monitoring the first derivative of the laser transmission through an absolute reference. In semiconductor lasers, this frequency dithering can be obtained easily by dithering the injection current. However, this dithering also modulates the laser output power. Here we show that this modulation of the laser output power results in an offset of the locked laser frequency from the reference frequency. We derive analytical expressions for these frequency offsets for semiconductor lasers frequency-locked to a Fabry-Perot transmission peak, a Gaussian absorption line, and a Lorentzian absorption line.     

Energy band structure of I–III–VI2 semiconductors

We review recent studies of the energy band structure of I-III-VI₂ semiconductors. The structure of the uppermost valence bands of a I-III-VI₂ compound is profoundly influenced by the proximity of noble metal d levels in the valence band. The direct energy gaps observed in I-III-VI₂ compounds are low relative to the energy gaps in the II–VI analogs by amounts up to 1.6eV, and the spin-orbit splittings observed in the ternaries are low relative to the values observed in the binary analogs, owing to a partial cancellation of the positive spin-orbit parameter for p levels and the negative spin-orbit parameter for d levels. The presence of the noble metal d levels in the valence band has been confirmed directly by the observation of electroreflectance structure due to transitions from the d levels themselves to the lowest conduction band minimum.     

Reversible and persistent electrical bistability in single crystals of a self-assembled pi-conjugated tetraaryl system: a submicrometer scale electrical characterization

A new pi-conjugated electroactive 4,4'-bipyridinium that bears two pyridazone self-complementary units was prepared and characterized. The new system readily assembles and forms at least two stable charge-transfer crystalline structures having a thermal population of unpaired electrons. The crystals of one phase exhibit electrical bistability, displaying either high (ON) and low (OFF) conductivity, at the same applied bias, depending on the electrical history of the system. The relation between the supramolecular structure of the crystals and their electrical properties is also discussed.