Characterization of Nanoscale Titanium Nitride Dispersions by Small-Angle Neutron Scattering

Suspensions of nanoscale titanium nitride (TiN) with a high solids content can be prepared by using guanidino propionic acid (GPA) as a stabilizing agent. The steric effect of an organic shell with polar groups on the surface of TiN spheres has been suggested in the literature as being a reason for the colloidal stability. To verify this hypothesis experimentally, we have performed small-angle neutron scattering (SANS) on this system; there is no evidence of an organic shell. Even at higher concentrations, in accordance with the Percus-Yevick theory, we could not observe any significant interparticular ordering. A plausible explanation for the stabilization of TiN suspensions is the buffer action of the amino acid GPA.     

A new concept for augmented van der Waals equations of state

A novel approach to perturbed equations of state for simple fluids is presented and its advantages over the traditional perturbed hard sphere equations are demonstrated by its application to several model fluids. The approach is based on a short range Yukawa reference which incorporates, in addition to repulsive interactions, also attractive interactions at short separations. The considered models of common interest are the Sutherland, Lennard-Jones, and EXP6 fluids. It is shown that using the proposed approach the reference system captures a good deal of properties of the studied fluids and that an accurate equation of state can be obtained using only the crude mean field (augmented van der Waals) approach.     

Femtosecond and Attosecond Electron Transfer Dynamics of Semiconductors Probed by the Core-Hole Clock Spectroscopy

Ultrafast electron transfer dynamics is a relevant topic to fundamental as well as many applied areas like femtochemistry, heterogeneous catalysis, surface photochemistry, molecular electronics, solar energy, among others. One way to probe it is through the resonant Auger spectroscopy (RAS), which provides a synchrotron radiation-based alternative to time-resolved optical spectroscopies in studying charge dynamics in the femtosecond and attosecond time regimes. RAS following core excitation presents major advantages: (i) the core-hole lifetime probed by core level spectroscopy can be used as a fast internal clock and insofar very low time scales in the range of femtoseconds (10^?15 s) down to hundred attoseconds (10^?18 s) can be achieved, the so-called core-hole clock (CHC) method; (ii) the inherent atomic specificity of core levels; and (iii) the surface sensitivity of low energy electrons adds further up. Here, the CHC approach will be presented and as an illustration of its use CHC results for a polymeric thin film will be discussed and compared with already existing data.

     

Pharmacologic actions of the second-generation leukotriene B4 receptor antagonist LY293111: in vitro studies

The in vitro actions were investigated of LY293111, a potent and selective leukotriene B4 (LTB4) receptor antagonist, on human neutrophils, human blood fractions, guinea pig lung membranes, and guinea pig parenchymal and tracheal strips. The IC50 for inhibiting [3H]LTB4 binding to human neutrophils was 17.6 +/- 4.8 nM. LY293111 inhibited LTB4-induced human neutrophil aggregation (IC50 = 32 +/- 5 nM), luminol-dependent chemiluminescence (IC50 = 20 +/- 2 nM), chemotaxis (IC50 = 6.3 +/- 1.7 nM), and superoxide production by adherent cells (IC50 = 0.5 nM). Corresponding responses induced by N-formyl-L-methionyl-L-leucyl-L-phenylalanine were inhibited by 100-fold higher concentrations of LY293111. LTB4 binding to guinea pig tissues and subsequent activation were also inhibited. The Ki for inhibition of [3H]LTB4 binding to lung membranes was 7.1 +/- 0.8 nM; IC50 for preventing binding of [3H]LTB4 to spleen membranes was 65 nM. The compound inhibited LTB4-induced contraction of guinea pig lung parenchyma. At 10 nM, LY293111 caused a parallel rightward shift of the LTB4 concentration-response curve. At higher concentrations, plots were shifted in a nonparallel manner, and maximum responses were depressed. LY293111 did not prevent antigen-stimulated contraction of sensitized trachea strips. At micromolar concentrations, LY293111 inhibited production of LTB4 and thromboxane B2 by plasma-depleted human blood stimulated with N-formyl-L-methionyl-L-leucyl-L-phenylalanine and thrombin. In addition, at these higher concentrations, formation of LTB4 by A23187-activated whole blood and conversion of arachidonic acid to LTB4 by a human neutrophil cytosolic fraction were inhibited. In summary, LY293111 is a second-generation LTB4 receptor antagonist with much improved potency in a variety of functional assay systems.     

Subchronic Toxicity of Copper Oxide Nanoparticles and Its Attenuation with the Help of a Combination of Bioprotectors

In the copper metallurgy workplace air is polluted with condensation aerosols, which a significant fraction of is presented by copper oxide particles <100 nm. In the scientific literature, there is a lack of their in vivo toxicity characterization and virtually no attempts of enhancing organism’s resistance to their impact. A stable suspension of copper oxide particles with mean (±SD) diameter 20 ± 10 nm was prepared by laser ablation of pure copper in water. It was being injected intraperitoneally to rats at a dose of 10 mg/kg (0.5 mg per mL of deionized water) three times a week up to 19 injections. In parallel, another group of rats was so injected with the same suspension against the background of oral administration of a “bio-protective complex” (BPC) comprising pectin, a multivitamin-multimineral preparation, some amino acids and fish oil rich in ω-3 PUFA. After the termination of injections, many functional and biochemical indices for the organism’s status, as well as pathological changes of liver, spleen, kidneys, and brain microscopic structure were evaluated for signs of toxicity. In the same organs we have measured accumulation of copper while their cells were used for performing the Random Amplification of Polymorphic DNA (RAPD) test for DNA fragmentation. The same features were assessed in control rats infected intraperitoneally with water with or without administration of the BPC. The copper oxide nanoparticles proved adversely bio-active in all respects considered in this study, their active in vivo solubilization in biological fluids playing presumably an important role in both toxicokinetics and toxicodynamics. The BPC proposed and tested by us attenuated systemic and target organs toxicity, as well as genotoxicity of this substance. Judging by experimental data obtained in this investigation, occupational exposures to nano-scale copper oxide particles can present a significant health risk while the further search for its management with the help of innocuous bioprotectors seems to be justified.     

Reasoning about places, times, and actions in the presence ofmobility

The current trend toward portable computing systems (e.g., cellular phones, laptop computers) brings with it the need for a new paradigm to facilitate thinking about and designing distributed applications. We use the term mobile to refer to distributed systems that include moving, autonomous agents which loosely cooperate to accomplish a task. The fluid nature of the interconnections among components of a mobile system provides new challenges and opportunities for the research community. While we do not claim to have fully grasped all the issues involved in specifying and modeling such systems, we believe that the notions of place, time, and action will play a central role in any model that is developed. We show that these concepts can be expressed and reasoned about in the UNITY logic with a minimal amount of additional notation. The formal derivation of a control system for a radio-dispatched elevator is used to show how considerations involving place, time, and actions impact the design process, be it formal or semiformal     

Stress Distribution in Rotating Solids with Frictional Heat Excited Over Contact Region

The present contribution is devoted to discussion of axially symmetric contact problems for two smooth solids, pressed against each other in relative rotation, generating heat due to the friction between them. We discuss and compared solutions for two extreme cases, namely when the unloaded surfaces of solids are thermally insulated, and when the heat exchange is so large that it is justified to assume that the temperature of the outside region of contact can be assumed zero. We prove that the distribution of contact pressure and the radius of contact region are the same in both the cases of thermal conditions. The thermal stresses, however, differ considerably. We analyze the distribution of the second invariant of the stress deviator, and we discuss the possibility of appearance of tensile stresses.     

Study and optimization of boronization in Alcator C-Mod using the Surface Science Station (S3)

A Surface Science Station (S³) on the Alcator C-Mod tokamak is used to study and optimize the location and rate of boron film deposition in situ during electron cyclotron (EC) discharge plasmas using 2.45 GHz radio-frequency (RF) heating and a mixture of helium and diborane (B₂D₆) gasses. The radial profile of boron deposition is measured with a pair of quartz microbalances (QMB) on S³, the faces of which can be rotated 360° including orientations parallel and perpendicular to the toroidal magnetic field B_T ～0.1 T. The plasma electron density is measured with a Langmuir probe, also on S³ in the vicinity of the QMBs, and typical values are ～1 × 10¹⁶ m^?3. A maximum boron deposition rate of 0.82 μg/cm²/min is obtained, which corresponds to 3.5 nm/min if the film density is that of solid boron. These deposition rates are sufficient for boron film applications between tokamak discharges. However the deposition does not peak at the EC resonance as previously assumed. Rather, deposition peaks near the upper hybrid (UH) resonance, ～5 cm outboard of the EC resonance. This has implications for RF absorption, with the RF waves being no longer damped on the electrons at the EC resonance. The previously inferred radial locations of critical erosion zones in Alcator C-Mod also need to be re-evaluated. The boron deposition profile versus major radius follows the ion flux/density profile, implying that the boron deposition is primarily ionic. The application of a vertical magnetic field (B_V ～0.01 T) was found to narrow the plasma density and boron deposition profiles near the UH resonance, thus better localizing the deposition. A Monte Carlo simulation is developed to model the boron deposition on the different QMB/tokamak surfaces. The model requires a relatively high boron ion gyroradius of ～5 mm, indicating a B⁺¹ ion temperature of ～2 eV, to match the deposition on QMB surfaces with different orientation to B_T. Additionally, the boron ion trajectories become de-magnetized at high neutral gas throughput (～0.5 Pa m³ s^?1) and pressure (～2 Pa) when the largest absolute deposition rates are measured, resulting in deposition patterns, which are independent of surface orientation to B_T in optimized conditions.