Experimental/analytical characterization of composite tubes under combined loading

The paper outlines the results of an investigation to characterize the response of P75/934 graphite/epoxy tubes with a stacking sequence of [15/0/±10/0/−15] _s under pure torsion and combined axial/torsion loading. The experimentally observed nonlinear response and path-dependent failure are discussed in terms of material nonlinearities at the ply level and first-ply failure loads with the help of an analytical model. Paper was presented at the 1989 SEM Spring Conference on Experimental Mechanics held in Cambridge, MA on May 28–June 1.     

Self‐assembly of polymer‐coated ferromagnetic nanoparticles into mesoscopic polymer chains

The self‐assembly of dispersed polymer‐coated ferromagnetic nanoparticles into micron‐sized one‐dimensional mesostructures at a liquid–liquid interface was reported. When polystyrene‐coated Co nanoparticles (19 nm) are driven to an oil/water interface under zero‐field conditions, long (≈ 5 μm) chain‐like assemblies spontaneously form because of dipolar associations between the ferromagnetic nanoparticles. Direct imaging of the magnetic assembly process was achieved using a recently developed platform consisting of a biphasic oil/water system in which the oil phase was flash‐cured within 1 s upon ultraviolet light exposure. The nanoparticle assemblies embedded in the crosslinked phase were then imaged using atomic force microscopy. The effects of time, temperature, and colloid concentration on the self‐assembly process of dipolar nanoparticles were then investigated. Variation of either assembly time t or temperature T was found to be an interchangeable effect in the 1D organization process. Because of the dependence of chain length on the assembly conditions, we observed striking similarities between 1D nanoparticle self‐assembly and polymerization of small molecule monomers. This is the first in‐depth study of the parameters affecting the self‐assembly of dispersed, dipolar nanoparticles into extended mesostructures in the absence of a magnetic field. © 2008 Wiley Periodicals, Inc.* J Polym Sci Part B: Polym Phys 46: 2267–2277, 2008     

Solid deuterium source of ultracold neutrons based on a pulsed spallation source

A new type of source of ultracold neutrons (UCNs) is proposed. The source operates on the basis of a pulsed spallation source. Solid deuterium makes it possible to obtain UCN density 10⁴ neutrons/cm³ as a result of high gain at low temperatures and the possibility of withstanding high pulsed heat loads as a result of the high specific heat of solid deuterium. Pis’ma Zh. éksp. Teor. Fiz. 66, No. 12, 765–770 (25 December 1997)     

Electron resonance spectra of some radicals derived from acetylenes and nitriles

The electron resonance spectra of a series of radicals derived by hydrogen abstraction from substrates containing carbon-carbon or carbon-nitrogen triple bonds have been studied in fluid solutions. The radicals ·CH₂CN, ·CH₂C ≡ CH and ·CH₂C ≡ C·CH₃ which have a linear heavy-atom framework show interesting temperature dependent line-width variations. These are attributed to spin-rotational interactions arising from anisotropic molecular reorientation. It is suggested that the motion about the long axis of these radicals is inertial in character.

The equilibrium geometries and hyperfine coupling constants of the propargyl and cyanomethyl radicals have been estimated from INDO-LCAO-SCF calculations.     

Effect of molecular structure on polyethylene melt rheology. I. Low-shear behavior

The melt rheological properties of both linear and branched polyethylene were investigated by use of narrow molecular weight distribution fractions and experimentally polymerized samples. Studies carried out in steady shear and in oscillatory shear yielded information concerning both the melt viscosity and the melt elasticity as a function of molecular structure, where the latter was characterized by various solution property techniques. The 3.4–3.5 power dependence of the low shear limiting viscosity on molecular weight was confirmed for linear polyethylene. The effect of long-chain branching on rheological properties was defined both at constant molecular weight and at constant molecular weight distribution and coupled with variation of molecular weight.     

Trace sulfide determination in oxic freshwaters

A simplified method for determination of reduced sulfur species in natural waters is presented. Reduced sulfur species were separated from a natural water matrix, using purge-and-trap (PT), after reacting with acid (acid volatile sulfide—AVS) or Cr(II) in acidic medium (chromium reducible sulfur—CRS). Sulfide in the trapping medium (0.05 M NaOH), was analyzed spectrophotometrically after derivatization to form methylene blue (MB). AVS precision for Na₂S and zinc sulfide clusters in synthetic solutions was ≤8.5% RSD at concentrations ranging from 48 to 503 nM. Spike recoveries of zinc sulfide clusters were 75-98% in a variety of freshwaters using the AVS procedure. Spike recoveries of Cu sulfide colloids were 94-109% in the same freshwater samples using the CRS procedure. During the analytical procedure an interfering compound was produced due to the reaction of mixed diamine reagent with itself. Lowering the pH of the reaction mixture minimized the formation of this compound. Minimizing contamination from particulates was necessary to achieve sub-nanomolar detection limits. The detection limit for AVS in a 500 ml sample with a 10 cm spectrophotometer cell was 0.1-0.3 nM (3×S.D. blank). The CRS procedure was calibrated with a synthetic CuS colloid. Interferences to the CRS method included finely divided pyrite, polysulfide, thiosulfate, sulfite and some elemental sulfur. The Cr(II) reagent did not reduce sulfate under our experimental conditions. The degree to which zinc sulfide clusters were adsorbed on membrane filters during filtration was mitigated if the clusters were synthesized in the presence of natural organic matter. Examples of AVS and CRS concentrations determined in oxygenated waters using the PT method were comparable to those reported recently by other methods. This method offers greater simplicity than other methods for trace dissolved sulfide determination in natural waters.     

Calculating the hopping times of confined fluids: two hard disks in a box

The dynamical transition between the anomalous single file diffusion of highly confined fluids and bulk normal diffusion can be described by a phenomenological model involving a particle hopping time tau(hop). We suggest a theoretical formalism that will be useful for the calculation of tau(hop) for a variety of systems and test it using a simple model consisting of two hard disks confined to a rectangular box with hard walls. In the case where the particles are moving diffusively, we find the hopping time diverges as a power law in the threshold region with an exponent of -(3/2). Under conditions where the particles move inertially, transition state theory predicts a power law behavior with an exponent of -2. Molecular dynamics simulations confirm the transition state theory result for inertial dynamics, while Brownian dynamics simulations suggest the scaling exponent is highly sensitive to the details of the algorithm.     

Determination of butyltin species in natural waters using aqueous phase ethylation and off-line room temperature trapping

Monobutyltin (MBT), dibutyltin (DBT) and tributyltin (TBT) were determined in natural water samples by aqueous phase ethylation with sodium tetraethylborate (STEB), room temperature trapping of the resulting volatile derivatives on Tenax TA^®, followed by gas chromatography-quartz furnace atomic absorption spectrometry (GC-QFAAS). Recoveries of butyltin spikes from natural water samples were 90-109% at concentrations of ∼100 ng Sn/l. The method precision at ∼100 ng Sn/l was ≤6% RSD for butyltins spiked into natural waters. The detection limits for 1 l water samples were <1 ng Sn/l for all butyltin species. Sample throughput of the method is high (greater than three samples per hour) due to the two-stage nature of the procedure, which allows derivatisation/trapping and GC-QFAAS quantitation to be performed separately. Off-line trapping is also advantageous as it extends the life of the GC column and quartz furnace to at least 12 months due to minimisation of carry-over of co-purged material.     

Azide addition to an endohedral metallofullerene: formation of azafulleroids of Sc3N@I(h)-C80

The reaction of an organic azide with an endohedral metallofullerene has been investigated for the first time. Isomeric [5,6]- and [6,6]-azafulleroids can be obtained from the thermal reaction of Sc(3)N@I(h)-C(80) with 4-isopropoxyphenyl azide, while photoirradiation leads exclusively to the [6,6]-azafulleroid. An unprecedented thermal interconversion between the two isomeric azafulleroids has also been discovered.