Vibration suppression of a cantilever beam using magnetically tuned-mass-damper

Eddy currents are induced by the movement of a conductor through a stationary magnetic field or a time varying magnetic field through a stationary conductor. These currents circulate in the conductive material and are dissipated, causing a repulsive force between the magnet and the conductor. These electromagnetic forces can be used to suppress the vibrations of a flexible structure. A tuned mass damper is a device mounted in structures to reduce the amplitude of mechanical vibrations and is one of the effective vibration suppression methods. In the present study, an improved concept of this tuned mass damper for the vibration suppression of structures is introduced. This concept consists of the classical tuned mass damper and an eddy current damping. The important advantages of this magnetically tuned mass damper are that it is relatively simple to apply, it does not require any electronic devices and external power, and it is effective on the vibration suppression. The proposed concept is designed for a cantilever beam and the analytical studies on the eddy current damping and its effects on the vibration suppression. To show the effectiveness of the proposed concept and verify the eddy current damping model, experiments on a cantilever beam are performed. It is found that the proposed concept could significantly increase the damping effect of the tuned mass damper even if not adequately tuned.     

Stereoselective synthesis of (−)-8-epi-swainsonine starting with a chiral aziridine

An efficient synthesis of (?)-8-epi-swainsonine, starting from a commercially available 1-(R)-α-methylbenzylaziridine-2-methanol, was developed. The synthetic route utilizes stereocontrolled Sharpless asymmetric dihydroxylation governed by AD-mix-β followed by an aziridine ring opening-cyclization sequence to generate the five membered N-heterocyclic ring system present in the bicyclic target. A subsequent stereoselective allylation and piperidine ring forming cyclization then produced a precursor that was converted into (?)-8-epi-swainsonine.     

Magnetization switching of CoFeSiB free-layered magnetic tunnel junctions

Magnetic tunnel junctions (MTJs) comprising amorphous Co_70.5Fe_4.5Si₁₅B₁₀, possessing low saturation magnetization of 560 emu/cm³, as a free layer have been investigated. The switching behaviours were confirmed for the micrometer-sized elements experimentally, using the scanning magneto-optical Kerr effect (scanning MOKE). A micromagnetic modelling study was also carried out for the submicrometer-sized elements. By using either a CoFeSiB single or a synthetic antiferromagnetic free-layer structure, the magnetization switching field became much lower than conventionally used CoFe free layered MTJs.     

An analytic valuation method for multivariate contingent claims with regime-switching volatilities

In this paper, we provide an analytic valuation method for European-type contingent claims written on multiple assets in a stochastic market environment. We employ a two-state Markov regime-switching volatility in order to reflect stochastically changing market conditions. The method is developed by exploiting the probability density of the occupation time for which the underlying asset processes are in a certain regime during a time period. In order to show its usefulness, we derive analytic valuation formulas for quanto options and exchange options with two underlying assets, as examples.     

A note on the stability of Jordan triple higher ring derivations

In the present paper, we establish the stability and the superstability of a functional inequality corresponding to the functional equation fn（xyx） = ∑i＋j＋k=n fi（x）fj （y）fk（x）. In addition, we take account of the problem of Jacobson radical ranges for such functional inequality.     

Diastereoselective cycloreductions and cycloadditions catalyzed by Co(dpm)(2)-silane (dpm = 2,2,6,6-tetramethylheptane-3,5-dionate): mechanism and partitioning of hydrometallative versus anion radical pathways

In the presence of phenylsilane and 5 mol % cobalt(II) bis(2,2,6,6-tetramethylheptane-3,5-dionate), aryl-substituted monoenone monoaldehydes and bis(enones) undergo reductive cyclization to afford syn-aldol and anti-Michael products, respectively. For both aldol and Michael cycloreductions, five- and six-membered ring formation occurs in good yield with high levels of diastereoselectivity. Cycloreduction of monoenone monoaldehyde 1a in the presence of d(3)-phenylsilane reveals incorporation of a single deuterium at the enone beta-position as an equimolar mixture of epimers, inferring rapid isomerization of the kinetically formed cobalt enolate prior to cyclization. The deuterated product was characterized by single-crystal neutron diffraction analysis. For bis(enone) substrates, modulation of the silane source enables partitioning of the competitive Michael cycloreduction and [2 + 2] cycloaddition manifolds. A study of para-substituted acetophenone-derived bis(enones) reveals that substrate electronic features also direct partitioning of cycloreduction and cycloaddition manifolds. Further mechanistic insight is obtained through examination of the effects of enone geometry on product stereochemistry and electrochemical studies involving cathodic reduction of bis(enone) substrates. The collective experiments reveal competitive enone reduction pathways. Enone hydrometalation produces metallo-enolates en route to aldol and Michael cycloreduction products, that is, products derived from coupling at the alpha-position of the enone. Electron-transfer-mediated enone reduction produces metallo-oxy-pi-allyls en route to [2 + 2] cycloadducts and, under Ni catalysis, homoaldol cycloreduction products, that is, products derived from coupling at the beta-position of the enone. The convergent outcome of the metal-catalyzed and electrochemically induced transformations suggests the proposed oxy-pi-allyl intermediates embody character consistent with the mesomeric metal-complexed anion radicals.     

Osmium tetroxide anchored to porous resins bearing residual vinyl groups: a highly active and recyclable solid for asymmetric dihydroxylation of olefins

[reaction: see text] OsO(4) was simply immobilized onto resins such as Amberlite XAD-4 or XAD-7 bearing residual vinyl groups. The resulting osmylated resins are air-stable, nonvolatile, and much easier to handle than their homogeneous counterpart (OsO(4)). Moreover, the resin-bound OsO(4) exhibited excellent catalytic activity in the asymmetric dihydroxylation of olefins and was easily recovered and reused in five consecutive reactions without any significant decrease in product yield. Turnover time, however, was significantly increased for the fourth and fifth reactions.     

Oxygen diffusion barriers using a new sacrificial design concept for future high-density memory devices

We emphasize the importance of the new design concept for diffusion barriers in high-density memory capacitors. RuTiN and RuTiO films are proposed as sacrificial oxygen diffusion barriers. They showed much lower sheet resistance up to 800 °C than various barriers including binary and ternary nitrides, reported by others. The contact resistance for both the Pt/RuTiN/TiSi_x/n⁺⁺poly-plug/n⁺channel layer/Si and the Pt/RuTiO/RuTiN/TiSi_x/n⁺⁺poly-plug/n⁺channel layer/Si contact structures, the most important electrical parameter for the diffusion barrier in the bottom-electrode structure of capacitors, exhibited values as low as 5 kΩ, even after annealing up to 750 °C. When each RuTiN and TiN film is inserted as a glue layer between the bottom electrode Pt layer in the CVD–BST simple stack-type structure, the thermal stability of the RuTiN glue layer is observed to be 150 °C higher than that of the TiN glue layer. Moreover, the capacitance of the PVD–BST simple stack-type structure with a TiN glue layer initially degrades after annealing at 500 °C, and thereafter failed completely. In the case of RuTiN and the RuTiO/RuTiN glue layers, however, the capacitance continuously increased up to 550 °C. These new experimental results accommodate the introduction of the sacrificial design concept of diffusion barriers against oxygen in high-density memory capacitors. Received: 6 February 2002 / Accepted: 4 March 2002 / Published online: 26 February 2003 RID="*" ID="*"Corresponding author. Fax: +82-31/360-4545, E-mail: dongsoo.yoon@hynix.com     

Laser-Induced Graphitic Carbon with Ultrasmall Nickel Nanoparticles for Efficient Overall Water Splitting

Metal nanoparticles encapsulated in graphitic carbon can show high catalytic efficiency and stability, yet the production method remains improved. Herein, it is demonstrated that a Ni-based metal–organic framework [EG-MOF-74(Ni)] can be rapidly transformed into ultrasmall Ni-nanoparticles with different sizes (4–11 nm) encapsulated in graphitic carbon via the laser-scribing method. The synthesized sample shows the best electrocatalytic performances with excellent stability in alkaline electrolyte for oxygen/hydrogen evolution reactions with overpotentials of 0.35/0.18 V at a current density of 10 mA cm⁻² when the Ni particle size is ≈6 nm. This is because of its well-developed micro/mesoporous structure, high electronic transport, and large electrochemical active surface area. An electrolyzer with Ni-nanoparticles encapsulated in the graphitic carbon shows a current density of 10 mA cm⁻² at a voltage of 1.6 V, which is comparable to the Pt/C and RuO₂ counterparts. The laser-based synthesis can serve as a powerful tool for the size-controlled synthesis of various catalysts out of MOFs.     

1,3,5‐Tri‐p‐tolyl­biuret

MoOCl₂(L_OMe) as catalyst, where L_OMe is CpCo[P(O)(OMe)₂]₃, reacts with p‐tolyl isocyanate to afford the title compound, C₂₃H₂₃N₃O₂. The structural features are the intramolecular hydrogen bond forming a six‐membered ring and a nearly planar arrangement of the biuret moiety. Each p‐tolyl phenyl ring is twisted by approximately 60–80° with respect to the others. The bond lengths N1—C22 of 1.357 (3) Å and N2—C23 of 1.333 (3) Å indicate that they are partial double bonds.