There has been continuing effort to understand the cause for the thickness dependence observed in the glass transition dynamics of polymer films. In a previous experiment, we showed that a two-layer model, assuming the films to contain a high-mobility surface layer residing on top of a bulklike inner layer, can explain the thickness dependence found in the viscosity of unentangled polystyrene films. Here, we examine the validity of this model in polystyrene films that are entangled. Unlike the unentangled films, the entangled ones are initially out-of-equilibrium, exhibiting a plateau modulus ∼1/10 times the bulk value. Upon annealing, the viscosity typically grows with time and eventually saturates. For the films with thickness above 20 nm, the saturated viscosity is the same as the bulk and takes ∼5–10 reptation times to reach. We find that the saturated viscosity is fully explainable by the two-layer model. A straightforward interpretation would imply that the surface mobile layer exists at equilibrium and modifies the dynamics of unentangled and entangled polymer films in a similar way.

Ultra-high energy neutrinos are detectable through impulsive radio signals generated through interactions in dense media, such as ice. Subsurface in-ice radio arrays are a promising way to advance the observation and measurement of astrophysical high-energy neutrinos with energies above those discovered by the IceCube detector (≥ 1 PeV) as well as cosmogenic neutrinos created in the GZK process (≥ 100 PeV). Here we describe the NuPhase detector, which is a compact receiving array of low-gain antennas deployed 185 m deep in glacial ice near the South Pole. Signals from the antennas are digitized and coherently summed into multiple beams to form a low-threshold interferometric phased array trigger for radio impulses. The NuPhase detector was installed at an Askaryan Radio Array (ARA) station during the 2017/18 Austral summer season. In situ measurements with an impulsive, point-source calibration instrument show a 50% trigger efficiency on impulses with voltage signal-to-noise ratios (SNR) of ≤2.0, a factor of ∼1.8 improvement in SNR over the standard ARA combinatoric trigger. Hardware-level simulations, validated with in situ measurements, predict a trigger threshold of an SNR as low as 1.6 for neutrino interactions that are in the far field of the array. With the already-achieved NuPhase trigger performance included in ARASim, a detector simulation for the ARA experiment, we find the trigger-level effective detector volume is increased by a factor of 1.8 at neutrino energies between 10 and 100 PeV compared to the currently used ARA combinatoric trigger. We also discuss an achievable near term path toward lowering the trigger threshold further to an SNR of 1.0, which would increase the effective single-station volume by more than a factor of 3 in the same range of neutrino energies. * Corresponding Author

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Originating from the early 1970s in Luleå, Sweden, and initially designed for the agricultural industry, hot-stamped sheet steel has developed to become the leading material in a modern state-of-the-art lightweight structural automotive body engineering. This critical review provides a detailed insight into the origins, fundamental metallurgical principles, commercial growth, current legal stronghold on aluminising coatings and latest technological developments. Comparisons to other state-of–the-art ferrous and non-ferrous automotive sheet materials are made, including carbon fibre-reinforced polymer; while the future outlook for hot-stamped sheet steel and opportunities for further technological developments are highlighted.

We study the effect of film preparation on the equilibration and viscoelastic properties of polymer films. Polystyrene films with a thickness of 14 nm are spun-cast from decalin solutions at different temperatures near the theta temperature to produce films with different chain conformations. We find that the equilibration time of the films increases significantly near the theta temperature. We attribute this to the onset of a rapid collapse in the polymer coil size at the theta condition, along with an increase in the solvent concentration in the films and thereby interchain separation at the time of vitrification. We find that these effects also cause the plateau modulus and equilibrium viscosity of the films to decrease.

Non-destructive testing is an important technique, and improvements are constantly needed. Surface defects in metals are not necessarily confined to orientations normal to the sample surface; however, much of the previous work investigating the interaction of ultrasonic surface waves with surface breaking defects has assumed cracks inclined at 90• to the surface. This paper explores the interaction of Rayleigh waves with cracks which have a wide range of angles and depths relative to the surface, using a non-contact laser generation and detection system. Additional insight is acquired using a 3D model generated using finite element method software. A clear variation of the reflection and transmission coefficients with both crack angle and length is found, in both the out-of-plane and in-plane components. The 3D model is further used to understand the contributions of different wavemodes to B-Scans produced when scanning a sample, to enable understanding of the reflection and transmission behaviour, and help identify angled defects. Knowledge of these effects is essential to correctly gauge the severity of surface cracking.

Solid-state NMR methods common to the analysis of polymers and other rigid solids are utilized for the study of kerogen, bitumen, and the organic content in source rocks. The use of straightforward nondestructive techniques, primarily employing solid-state NMR, is shown to provide useful information about both individual samples and changes between samples that cover a range of thermal maturities of type II kerogen. In addition to aromatic fraction and chemical structure, one of the most striking changes to isolated kerogen with maturity is the distribution of pore sizes, studied with both 129Xe NMR and complementary nitrogen physisorption, that may help to understand the process of bitumen generation. Ultimately, direct in situ analysis of source rock samples that allow kerogen and bitumen to be distinguished is desirable, as it would eliminate the time and effort to isolate and prepare kerogen samples. By proper consideration and removal of the background, we find that a clear 13C NMR signal can be obtained from source rock with total organic carbon weight as low as 2%. Simple 1H NMR methods are shown to quickly provide a qualitative measurement of the bitumen in source rocks, while 13C cross-polarization is found to be an easy method to distinguish kerogen from bitumen.

Numerous studies have shown that the glass transition temperature, T g , of polymers may change visibly upon addition of even small amounts of nanoparticles. In this study, we examine the effect of polymer−nanoparticle interfacial energy on this phenomenon in nanocomposite films containing polystyrene-grafted nanoparticles mixed with polystyrene homopolymer at low particle loadings. A previous experiment showed that the interfacial energy of this system modulates with the grafting density of the grafted polymer and the molecular weight ratio of the matrix and grafted polymers. We find that the changes in T g vary with both parameters in manners that quantitatively agree with the interfacial energy.