The use of stress for the control of magnetic anisotropy in amorphous FeSiBC thin films: a magneto-optic study

Magnetostrictive FeSiBC amorphous thin films based on the METGLAS^® 2605SC composition have been produced by RF magnetron sputtering. The magnetic properties were investigated using the magneto-optical Kerr effect, with both point hysteresis measurements and domain imaging. Significant in-plane anisotropy is observed in the as-grown samples, which was attributed to the residual field from the magnetron sputter source. The effects of various treatments on the samples were investigated, including the use of forming fields, stress, and thermal processing. The deliberate introduction of stress into these materials is found to allow excellent control of both the direction and magnitude of magnetic anisotropy, and can also be used as a novel method for the absolute measurement of magnetostriction. The treatments are evaluated for their potential to control anisotropy in magnetostrictive device applications.     

Continuum limit of overlap valence quarks on a twisted mass sea

We study a lattice QCD mixed action with overlap valence quarks on two flavours of Wilson maximally twisted mass sea quarks. Employing three different matching conditions to relate both actions to each other, we investigate the continuum limit by using three values of the lattice spacing ranging from a≈0.05 fm$a\approx 0.05\text{fm}$ to 0.08 fm$0.08\text{fm}$. A particular emphasis is put on the effect on physical observables of the topological zero modes appearing in the valence overlap operator. We estimate the region of parameter space where the contribution from these zero modes is sufficiently small such that their effects can be safely controlled and a restoration of unitarity of the mixed action in the continuum limit is reached.     

Tapered fiber optic surface plasmon resonance sensor for analyses of vapor and liquid phases

We report a new approach to analyze both vapor and liquid phases by utilizing a tapered fiber optic surface plasmon resonance (SPR) probe. This technique employs a fiber optic SPR probe with a modified geometry to tune the SPR coupling wavelength-angle pair. The observed composite spectrum included two distinct SPR dips associated with surface plasmons excited in the gas and liquid active regions. This sensor is able to detect refractive index changes in both vapor and liquid phases individually by simultaneous monitoring SPR coupling wavelengths from the two sensing surfaces.     

X-Band Pulsed ENDOR Study ofFe-Substituted Sodalite— The Effect of the Zero-Field Splitting

X-band (∼9.3 GHz) pulsed ENDOR measurements were carried out on⁵⁷Fe-substituted sodalite (FeSOD) which contains only one type of Fe(III) (S=) located at a framework site. The ENDOR spectrum recorded atg= 2 shows three doublets corresponding to the sixM_Smanifolds. The assignment of these signals was confirmed by hyperfine-selective and triple ENDOR experiments. The components of each of the doublets had different intensities, reflecting the different populations of the EPR energy levels at the measurement temperature, 1.8 K. ENDOR spectra were recorded at magnetic fields within the EPR powder pattern, and the field dependence observed showed an anisotropic behavior, unexpected from the isotropic character of the⁵⁷Fe(III) hyperfine coupling. This dependence was attributed to the high-order effects of the zero-field splitting (ZFS) interaction on the ENDOR frequencies. Three different theoretical approaches were used to account for the dependence of the ENDOR spectrum on the ZFS interaction. The first involves the exact diagonalization of the total spin Hamiltonian, the second uses third-order perturbation approximations, and the third employs an effective nuclear Hamiltonian for each of theM_Smanifolds. The simulations showed that the ENDOR signals of theM_S= ±5/2 (ν_±5/2) manifold are the least sensitive to the magnitude of the ZFS parameterDand are therefore the most appropriate for the determination ofa_iso. It is shown that at X band anda_isovalues of about 30 MHz, the perturbation approach is valid up toDvalues of 500 MHz if all three doublets are concerned. However, if only the ν_±5/2doublet is considered, then this approach is valid forD< 1000 MHz. The third approach was found inappropriate fora_isovalues of ∼30 MHz. Using the method of exact diagonalization together with orientation selectivity, the trends observed in the experimental spectra could be reproduced. The ENDOR spectra of the⁵⁷Fe-substituted zeolites ZSM5, L, and mazzite showed broad and ill-defined peaks since the ZFS of Fe(III) in these zeolites is significantly larger than that of FeSOD. Because this broadening is a high-order effect, it can be significantly reduced at higher spectrometer frequencies.     

Constraints on dark matter annihilation from M87

As the largest mass concentrations in the local Universe, nearby clusters of galaxies and their central galaxies are prime targets in searching for indirect signatures of dark matter annihilation (DMA). We seek to constrain the dark matter annihilation emission component from multi-frequency observations of the central galaxy of the Virgo cluster. The annihilation emission component is modeled by the prompt and inverse-Compton gamma rays from the hadronization of annihilation products from generic weakly interacting dark matter particles. This component is fitted to the excess of the observed data above the spectral energy distribution (SED) of the jet in M87, described with a best-fit synchrotron-self-Compton (SSC) spectrum. While this result is not sufficiently significant to claim a detection, we emphasize that a dark matter “double hump signature” can be used to unambiguously discriminate the dark matter emission component from the variable jet-related emission of M87 in future, more extended observation campaigns.     

Driven depinning of strongly disordered media and anisotropic mean-field limits

Extended systems driven through strong disorder are modeled generically using coarse-grained degrees of freedom that interact elastically in the directions parallel to the drive and slip along at least one of the directions transverse to the motion. In the limit of infinite-range elastic and viscous coupling this model has a tricritical point separating a region where the depinning is continuous, in the universality class of elastic depinning, from a region where depinning is hysteretic. Many of the collective transport models discussed in the literature are special cases of the generic model.     

Modeling the acoustic radiation force in microfluidic chambers

A procedure is demonstrated to quantitatively evaluate the acoustic radiation forces in microfluidic particle manipulation chambers. Typical estimates of the acoustic pressure and the acoustic radiation force are based on an analytical solution for a simple one-dimensional standing wave pattern. The complexities of a typical microfluidic channel limit the usefulness of this approach. By leveraging finite elements, and a generalized equation for the acoustic radiation force, channel designs can be investigated in two and three dimensions. Calculations and experimental observations in this report and the literature, confirm these claims.     

Insights into the oxidation of propylene oxide through the analysis of experiments and kinetic modeling

Cyclic ethers are important intermediates in the oxidation of hydrocarbons and biofuels. Studying the oxidation and pyrolysis of cyclic ethers will help in improving our understanding of this functional group and provide consistency to the base mechanism where they play an important role. In this aspect, propylene oxide has been investigated in this study by obtaining ignition delay time measurements in the rapid compression machine and shock tube. The experiments were performed in a range of pressures varying from 10 to 40 bar at different equivalence ratios (0.5–2.0) and dilution percentages. Additionally, speciation measurements in the shock tube at pyrolysis conditions have been performed at a pressure of 40 bar to explore the isomerization pathways. A detailed kinetic mechanism was developed to describe both the oxidation and pyrolysis chemistry of propylene oxide. The mechanism is not only able to predict the data obtained from this study but also reproduces the data from the literature in a consistent trend. For a better understanding of the oxidation and pyrolysis chemistry of propylene oxide, the kinetic analyses were performed using the developed mechanism to comprehend the important reaction pathways and sensitive reactions. At the investigated regime, the consumption of propylene oxide through its isomerization channels is the critical pathway that controls the reactivity of the fuel.