Demagnetization in photomagnetic films

We present a model for demagnetization in photomagnetic films, and investigate different regimes for the magnetizing process using finite element analysis. It is found that the demagnetizing factor may depend strongly upon the high-spin fraction of the film, and the specifics of the dependence are dictated by the microscopic morphology of the photomagnetic domains. This picture allows for facile interpretation of existing data on photomagnetic films, and can even explain an observed photoinduced decrease in low-field magnetization concurrent with increase in high-spin fraction. As a whole, these results reiterate the need to consider demagnetizing effects in photomagnetic films.     

N‐Acetyl‐l‐phenyl­alanine

The structure of the title compound, C₁₁H₁₃NO₃, is characterized by a two‐dimensional infinite network of intermolecular N—H?O and O—H?O hydrogen bonds.     

Small momentum transfer measurements of S(k) in 4He at T = 4.27 K as function of density

We report the first measurements of S(k) in ⁴He at a fixed temperature of T = 4.27 K for 126 < p < 164 kg/m³ for the momentum transfer range $\text{0.18 < k < 1.03}\text{A}\text{?}{}^{\mathrm{?1}}$. Our results are consistent with expectations at zero momentum transfer based on thermodynamics.     

Superfluid Avalanches in Nuclepore: Constrained versus Free-Boundary Experiments and Simulations

Superfluid 4He exhibits hysteretic behavior in the percolated nanoporous material Nuclepore during the filling and draining of pores due to capillary condensation, and one observes avalanches during the pore draining. We observe that the size and frequency of the avalanches depend upon whether the fluid flow off the substrate during draining is impeded or unimpeded. We simulate the draining of superfluid 4He from Nuclepore with and without a perturbation of the pore menisci and find results similar to the results seen in the experiments in the presence or the absence of flow inhibition.     

Kosterlitz-Thouless transition for 4He films adsorbed to rough surfaces

We report the study of adsorption isotherms of 4He on several well characterized rough CaF2 surfaces using a quartz crystal microbalance technique at 1.672 K. The signature of decoupled mass observed on crossing the Kosterlitz-Thouless transition as a function of 4He film thickness decreases and becomes increasingly difficult to identify as the surface roughness is increased. A peak in the dissipation, indicative of the onset of superfluidity, changes little with roughness.     

Thinning of saturated superfluid 4He films during critical and subcritical flow

We report measurements of the thickness of a saturated superfluid ⁴He film under conditions of both critical and subcritical flow. Thinning consistent to within 20% with the predictions of Kontorovich as applied to our apparatus is observed over the temperature range 1.2 < T < 1.6 K. The results appear to rule out critical flow effects as an explanation of Keller's results.     

Exposure to nanoscale particles and fibers during machining of hybrid advanced composites containing carbon nanotubes

This study investigated airborne exposures to nanoscale particles and fibers generated during dry and wet abrasive machining of two three-phase advanced composite systems containing carbon nanotubes (CNTs), micron-diameter continuous fibers (carbon or alumina), and thermoset polymer matrices. Exposures were evaluated with a suite of complementary instruments, including real-time particle number concentration and size distribution (0.005–20 μm), electron microscopy, and integrated sampling for fibers and respirable particulate at the source and breathing zone of the operator. Wet cutting, the usual procedure for such composites, did not produce exposures significantly different than background whereas dry cutting, without any emissions controls, provided a worst-case exposure and this article focuses here. Overall particle release levels, peaks in the size distribution of the particles, and surface area of released particles (including size distribution) were not significantly different for composites with and without CNTs. The majority of released particle surface area originated from the respirable (1–10 μm) fraction, whereas the nano fraction contributed ~10% of the surface area. CNTs, either individual or in bundles, were not observed in extensive electron microscopy of collected samples. The mean number concentration of peaks for dry cutting was composite dependent and varied over an order of magnitude with highest values for thicker laminates at the source being >1 × 10⁶ particles cm⁻³. Concentration of respirable fibers for dry cutting at the source ranged from 2 to 4 fibers cm⁻³ depending on the composite type. Further investigation is required and underway to determine the effects of various exposure determinants, such as specimen and tool geometry, on particle release and effectiveness of controls.