Almost Complete Transmission of Waves Through Perforated Cross-Walls in a Waveguide with Dirichlet Boundary Condition

Siberian Mathematical Journal - We consider a waveguide composed of two not necessity equal semi-infinite strips (trunks) and a rectangle (resonator) connected by narrow openings...     

T-coercivity and continuous Galerkin methods: application to transmission problems with sign changing coefficients

To solve variational indefinite problems, one uses classically the Banach–Ne?as–Babu?ka theory. Here, we study an alternate theory to solve those problems: T-coercivity. Moreover, we prove that one can use this theory to solve the approximate problems, which provides an alternative to the celebrated Fortin lemma. We apply this theory to solve the indefinite problem $\text{ div}\sigma \nabla u=f$ set in $H^1_0$ , with $\sigma $ exhibiting a sign change.     

Probing complex materials with coherent soft X-rays

We motivate the use of coherent soft X-ray beams to study materials that exhibit complex nanoscale behaviors. A new beamline and magnetic scattering end station that has been constructed and commissioned at the ALS will be described. Finally, we present some initial results that indicate the performance of the beamline. K. Chesnel now at Department of Physics, Brigham Young University, Provo, Utah, USA. J.J. Turner now at Department of Physics, Stony Brook University, Stony Brook, New York, USA. M. Pfeifer now at School of Physics La Trobe University, Melbourne, Australia.     

Anomalous Wave Transmission through a Thin Channel Connecting Two Acoustic Waveguides

Doklady Physics - In this paper, we find a criterion for to remove almost complete transmission of the piston mode from one semi-infinite waveguide to another one through a thin connecting channel...     

Dissociative ionization of the H2O molecule bombarded by swift singly charged and slow highly charged ions

Fragment ion energy spectra of the water molecule have been measured in conventional crossed-beam experiments by the impact of 46 keV/u energy, singly charged ions (SCIs) and 4.3 keV/u energy, highly charged ions (HCIs). Double differential cross sections have been determined and a comparative analysis has been performed. We found that the fragmentation spectra for SCIs and HCIs are very similar, indicating that both collisions lead to the same fragmentation channels. This suggests that the Coulomb explosion of the water molecule is dominantly determined by the charge state of the transient molecular ions, and it is almost independent from the primary ionization mechanism. Differences were observed not only between the SCI and HCI impact-induced fragmentation cross sections, but between those obtained by the 60 keV N⁶⁺ and 70 keV O⁷⁺ projectiles. The differences were attributed to the selectivity of the electron capture process for HCIs. Multiple target ionization cross sections have been deduced from the fragment ion spectra. We found contributions of up to fivefold ionization for SCIs and up to sixfold ionization for HCIs.     

Combined neutron and synchrotron studies of magnetic films

We discuss specular reflectivity and off-specular scattering of neutrons and X-rays from magnetic films. Both these techniques are capable of providing information about the morphology of the chemical and magnetic roughness and the magnetic domain structure. The use of neutrons with polarization analysis enables the spatial distribution of different vector components of the magnetization to be determined, and the use of resonant magnetic X-ray scattering enables magnetization in a compound system to be determined element-selectively. Thus both these methods provide powerful and complementary new probes for studying magnetism at the nanoscopic level in a variety of systems such as those exhibiting exchange bias, giant magnetoresistance, spin injection, etc. We shall illustrate with an example of both techniques applied to an exchange bias system consisting of a single crystal of antiferromagnetic FeF₂ capped with a ferromagnetic Co film, and discuss what has been learned about how exchange bias works in such a system.