Crystallization characteristics of amorphous Fe-Si-B alloys

Crystallization of soft magnetic Fe-Si-B glasses was investigated by transmission electron microscopy and X-ray diffraction. Electron micrographs of the successive crystallization stages of some Fe-Si-B glasses were obtained and the morphology variations for different alloy compositions were determined. The compositional dependence of the crystallization mode exhibited by the Fe-Si-B glasses was analysed, and on this basis some suggestions about crystallization rules in these glasses are proposed. Two kinds of iron—silicon phases occurred, depending on the Fe-Si-B alloy composition: bcc Fe(Si) solid solution and an ordered solid solution on the structural basis of Fe₃Si iron suicide. It is suggested that the metastable Fe₃B phase (observed during crystallization of only few glasses) was not a simple consequence of boron content. Crystallization of the Fe₃B phase was related to the formation of the iron—silicon phase which was produced during the first crystallization stage.     

Shear and membrane locking in curved C0 elements

Locking phenomena in C⁰ curved finite elements are studied for displacement, hybrid-stress and mixed formulations. It is shown that for a curved beam element, shear and membrane locking are interrelated and either shear or membrane underintegration can alleviate it. However, reduced shear integration tends to diminish the membrane-flexural coupling which characterizes curved elements. Locking can also be expected in certain types of mixed formulations, the hybrid-stress formulations avoids locking for beams (but not for shells). Methods for avoiding locking are explored and alternatives evaluated.     

Combined Short-Path Distillation and Solvent-Assisted Crystallization of Beef Fatty Acid Methyl Esters

Solvent‐assisted crystallization has previously been employed to remove long‐chain saturated fatty acids (≥ 18 carbons) from animal fat to improve its cold temperature biofuel properties. The same technology can be used for removing long‐chain saturated fatty acids (SFA) from animal fats for human consumption, but SFA remaining (i.e., 14:0 and 16:0) are more atherogenic than longer chain SFA. In the present study, an easy and efficient method was developed using short‐path distillation prior to solvent‐assisted crystallization for the more complete removal of SFA from beef tallow, and for the first time reports the distillation and crystallization behavior of polyunsaturated fatty acid biohydrogenation products (PUFA‐BHP). Shorter chain SFA methyl esters (i.e., 14:0 and 16:0) were efficiently removed at 90 °C, 9.3 Pa, with a rotor speed of 70 rpm and either two cycles of distillation at 90 drops/min or three cycles at 110 drops/min. Stearic acid (18:0) was then effectively removed by crystallization at ?20 °C using a sample to methanol ratio of 1:10. The remaining fraction enriched with PUFA‐BHP (i.e., rumenic acid, c9,t11‐18:2, and its precursor vaccenic acid, t11‐18:1) have potential use in disease model (i.e., cell culture and animal) studies to help further elucidate their bioactivity and mode of action, and may in the future have functional food or nutraceutical potential.     

Multiphase Biomineralization: Enigmatic Invasive Siliceous Diatoms Produce Crystalline Calcite

Diatoms are considered unicellular eukaryotic organisms exclusively depositing biogenic silica. Heretofore there has been no report of calcification by these algae. Here it is shown that calcium carbonate within the stalks of Didymosphenia geminata, a nuisance species that has prolifically colonized streams and rivers globally, is biogenic in origin and occurs as a network of calcite nanofibers. The nanofibrous framework in the mineralized polysaccharide matrix imparts mechanical support to the stalks, providing stability in variable flow conditions. The results demonstrate that D. geminata possesses cellular and periplasmic carbonic‐anhydrases that contribute to carbon fixation and biomineralization, respectively. The activity of external carbonic‐anhydrase was more than 50% of the total activity, which points to its role in anchoring this bioeroding diatom on hard surfaces. The first evidence of multiphase biomineralization by diatoms that deposit both biogenic silica and crystalline biogenic calcite which are imparting distinct functional advantage to the organism is provided.     

Mid-ultraviolet light-emitting diode detects dipicolinic acid

Dipicolinic acid (DPA, 2,6-pyridinedicarboxylic acid) is a substance uniquely present in bacterial spores such as that from anthrax (B. anthracis). It is known that DPA can be detected by the long-lived fluorescence of its terbium chelate; the best limit of detection (LOD) reported thus far using a large benchtop gated fluorescence instrument using a pulsed Xe lamp is 2 nM. We use a novel AlGaN light-emitting diode (LED) fabricated on a sapphire substrate that has peak emission at 291 nm. Although the overlap of the emission band of this LED with the absorption band of Tb-DPA (lambda(max) doublet: 273, 279 nm) is not ideal, we demonstrate that a compact detector based on this LED and an off-the-shelf gated photodetection module can provide an LOD of 0.4 nM, thus providing a basis for convenient early warning detectors.     

Bang–Bang Refocusing of a Qubit Exposed to Telegraph Noise

Solid state qubits promise the great advantage of being naturally scalable to large quantum computer architectures, but they also possess the significant disadvantage of being intrinsically exposed to many sources of noise in the macroscopic solid-state environment. With suitably chosen systems such as superconductors, many of sources of noise can be suppressed. However, imprecision in nanofabrication will inevitably induce defects and disorder, such as charged impurities in the device material or substrate. Such defects generically produce telegraph noise and can hence be modelled as bistable fluctuators. We demonstrate the possibility of the active suppression of such telegraph noise by bang–bang control through an exhaustive study of a qubit coupled to a single bistable fluctuator. We use a stochastic Schrödinger equation, which is solved both numerically and analytically. The resulting dynamics can be visualized as diffusion of a spin vector on the Bloch sphere. We find that bang–bang control suppresses the effect of a bistable fluctuator by a factor roughly equalling the ratio of the bang–bang period and the typical fluctuator period. Therefore, we show the bang–bang protocol works essentially as a high pass filter on the spectrum of such telegraph noise sources. This suggests how the influence of 1/f-noise ubiquitous to the solid state world could be reduced, as it is typically generated by an ensemble of bistable fluctuators. Finally, we develop random walk models that estimate the level of noise suppression resulting from imperfect bang–bang operations, such as those that cannot be treated as -function impulses and those that have phase and axis errors. PACS: 03.65.Yz, 03.67.Lx, 05.40.-a     

The Peculiarities of Magnetic Flux Dynamics at Magnetothermal Instability in Textured Bi2Sr2CaCu2O8+δ

The magnetic flux dynamics was investigated in a textured Bi₂Sr₂CaCu₂O₈₊ sample using a miniature Hall probe placed on the surface of the superconductor. The process of magnetic flux penetration into the superconductor was found to have a complex structure and consist of two processes with different time scales. The first one has a length of tens of microseconds and is considered as locally adiabatic. The second one has a length comparable with the time of thermal diffusion. The importance of the above two processes in the development of magnetic instability is analyzed.     

Application of space periodic variation of light polarization in imaging polarimetry

The application of space periodic variation of light polarization for measurement and calculation of the distribution of the phase retardation between two eigenwaves propagating inside a linearly birefringent media and the distribution of the azimuth angle of the first eigenvector is described. The measuring method proposed does not require any mechanical movements or rotations of any optical elements. Application of a liquid crystal (LC) modulator instead of a quarter-wave plate gives an opportunity to introduce the required phase shift. The space periodic modulation of the polarization of light is achieved by the use of a Wollaston prism placed inside the path of the light beam. Then a fast Fourier transform is used for further calculations. The number of measurements of the light intensity at the output of the system is minimized to two. These assumptions make the proposed method very fast, which is especially important in measurements of the objects with optical anisotropy that is changing in time.