Radioxenon signatures from activation of environmental xenon

For distinguishing between nuclear explosions and other man made releases, atmospheric monitoring of radioactive noble gas isotopes, xenon isotopes in particular, is of interest to the non-proliferation community. Radioxenon releases can originate from nuclear weapons tests (atmospheric, underground, and underwater), research and commercial reactors, and medical isotope production facilities. Their impacts on atmospheric sample analysis have to be well understood to distinguish between them. This work focuses on the contribution of xenon activation by thermal, epithermal, and 14 MeV neutrons to radioxenon signatures. Calculations to estimate radioxenon production from activation in research reactors are performed and compared to experimental data.     

2,4,6‐trichlorophenyl acrylate emulsion‐templated porous polymers (PolyHIPEs). Morphology and reactivity studies

A series of monolithic crosslinked polymers with 2,4,6‐trichlorophenyl acrylate as a reactive component was prepared by free radical polymerization of the internal phases of high internal phase emulsions (HIPEs). The volume ratio of water to oil phase (void volume; 60–90%), crosslinker type (divinylbenzene or ethylenglycol dimethacrylate) and quantity (30–50 mol %) and type of porogenic solvent (chlorobenzene, toluene, chloroform, dichloroethane) were altered to study these effects on the structure and reactivity of the monolithic polymers. The polymer supports were characterized by scanning electron microscopy (SEM), FTIR spectroscopy, elemental analysis and mercury intrusion porosimetry. SEM images revealed an open cellular structure with voids between 1 and 12 μm and window sizes between 0.3 and 3 μm. The porogen had an influence on the surface area, being larger with added porogen and the influence being highest with toluene. Adding toluene also influenced the void size, increasing the average diameter from ～2 μm (no porogen) to ～12 μm (added toluene). Monolithic supports were functionalized by reaction of the ester moieties with tris(2‐aminoethyl)amine derivative and by hydrolysis of the ester groups to carboxylic acids. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4043–4053, 2007     

A magnet spring model

The paper discusses an elementary spring model representing the motion of a magnet suspended from the ceiling at one end of a vertical spring which is held directly above a second magnet fixed on the floor. There are two cases depending upon the north–south pole orientation of the two magnets. The attraction or repelling force induced by the magnets follow an inverse quartic law and thus we are led to a nonlinear model suitable for discussion in a beginning differential equations course. Spring models are common fare in such courses, but usually only linear models with simple sinusoidal forcing are considered. The resultant model is autonomous and thus an energy approach permits a full phase portrait of the resultant motions in the phase plane. These phase portraits show interesting behaviour of the system, reinforcing one's natural physical intuition. The computer algebra system Mathematica is employed here, although almost any other system would suffice. Such a system permits almost effortless calculations and can generate the graphics needed to thoroughly investigate the model.     

Effect of the oligothiophene chain length on the performance of organic photovoltaic cells

We investigate photovoltaic cells based on α-oligothiophene molecules with different chain lengths nT (n=4,6,8) deposited on a sandwich structure between two electrodes: ITO and Al. From the analysis of the absorption and photocurrent spectrum, we have shown that the structure of the oligothiophene affects considerably the absorbing character of the evaporated film, which is increasingly significant from 4T towards 8T, and a significant photocurrent in agreement with strong absorption in the region Al/nT. Moreover, a theoretical model of Ghosh is used to display the photocurrent origin, proved to be sufficient after adjustment with a random term. Then we deduce that the crystalline order of the film improves the transport of charge and the photocurrent. The results are confirmed by electrical characterization under illumination that shows effectively an influence of the expansion of the molecular chains on the increase in the energy efficiencies and on the performances of organic photovoltaic cells.     

Atomic layer deposition of HfO2 on graphene from HfCl4 and H2O

Atomic layer deposition of HfO₂ on unmodified graphene from HfCl₄ and H₂O was investigated. Surface RMS roughness down to 0.5 nm was obtained for amorphous, 30 nm thick hafnia film grown at 180°C. HfO₂ was also deposited in a two-step temperature process where the initial growth of about 1 nm at 170°C was continued up to 10–30 nm at 300°C. This process yielded uniform, monoclinic HfO₂ films with RMS roughness of 1.7 nm for 10–12 nm thick films and 2.5 nm for 30 nm thick films. Raman spectroscopy studies revealed that the deposition process caused compressive biaxial strain in graphene, whereas no extra defects were generated. An 11 nm thick HfO₂ film deposited onto bilayer graphene reduced the electron mobility by less than 10% at the Dirac point and by 30–40% far away from it.     

In Situ Coupling of Single Molecules Driven by Gold‐Catalyzed Electrooxidation

A single‐molecule method has been developed based on the scanning tunneling microscope (STM) to selectively couple a series of aniline derivatives and create azobenzenes. The Au‐catalyzed oxidative coupling is driven by the local electrochemical potential at the nanostructured Au STM tip. The products are detected in situ by measuring the conductance and molecular junction elongation and compared with analogous measurements of the expected azobenzene derivatives prepared ex situ. This single‐molecule approach is robust, and it can quickly and reproducibly create reactions for a variety of anilines. We further demonstrate the selective synthesis of geometric isomers and the assembly of complex molecular architectures by sequential coupling of complementary anilines, demonstrating unprecedented control over bond formation at the nanoscale.     

Acceptance inspection by variables when the measurements are subject to error

The situation considered is that in which measurement of the characteristic of interest is not exact but subject to appreciable error. The error is assumed to be unbiased and independent of the actual value of the characteristic measured. The population and error variances,σ ² andσ _e ² , are assumed to be such thatσ/σ _e has a known lower limit which is greater than zero. The probability distributions involved are assumed to be normal while the actual values and measurement errors each form a random sample. For suitable specified acceptable and unacceptable fractions defective, and forσ _e assumed known and unknown, this paper presents one-sided acceptance inspection criteria which are optimum in a specified sense, and which have the property that the producer’s and consumer’s risks have specified upper bounds.     

Tin/Indium nanobundle formation from aggregation or growth of nanoparticles

Shape and size controlled gram level synthesis of tin/indium (SnIn) alloy nanoparticles and nanobundles is reported. Poly(N-vinylpyrrolidone) (PVP) was employed as a capping agent, which could control the growth and structure of the alloy particles under varying conditions. Transmission electron microscopy showed that unique SnIn alloy nanobundles could be synthesized from the bulk materials above a certain concentration of PVP and below this concentration, discrete spherical nanoparticles of variable size were evolved. The morphology and the composition of the as-synthesized SnIn alloy nanobundles were investigated by high-resolution transmission electron microscopy (TEM). The possible mechanisms on the formation of these structures were discussed.