Tuning the metal-adsorbate chemical bond through the ligand effect on platinum subsurface alloys

Scratching beneath the surface: Pt-M(3d)-Pt(111) (M(3d) = Co, Ni) bimetallic subsurface alloys have been designed to show the ligand effect tunes reactivity in oxygen and hydrogen adsorption systems. The platinum-oxygen bond order was investigated by oxygen atom projection in the occupied and unoccupied space using X-ray emission spectroscopy (XES) and X-ray absorption spectroscopy (XAS).     

Control of the dynamic response of a damped membrane by distributed forces

The problem of damping out the oscillations of a rectangular membrane by means of distributed forces is solved analytically. The membrane may be subject to viscous damping and is clamped along the boundaries. The motion of the membrane is initiated by given initial displacement and velocity conditions. The basic control problem is to minimize the deflection and the velocity of displacements in a given period of time with the minimum possible expenditure of force. A quadratic vector performance index is chosen as the cost functional which comprises the functionals of the deflection, velocity and the distributed force. The necessary conditions of optimality are obtained from a control theory approach and formulated in the form of a maximum principle in terms of an adjoint variable. The multi-objective control formulation permits the decision maker to shift the weight of the control to the minimization of any one of the quantities of interest and explore the optimum capabilities of the structural element. Numerical results are given for various problem parameters and the efficiency of the control mechanism is investigated. The optimal tradeoff curves, which represent the points of optimum performance, are given for a couple of example problems with multiple objectives.     

Optimal boundary control of dynamics responses of piezo actuating micro-beams

Optimal control theory is formulated and applied to damp out the vibrations of micro-beams where the control action is implemented using piezoceramic actuators. The use of piezoceramic actuators such as PZT in vibration control is preferable because of their large bandwidth, their mechanical simplicity and their mechanical power to produce controlling forces. The objective function is specified as a weighted quadratic functional of the dynamic responses of the micro-beam which is to be minimized at a specified terminal time using continuous piezoelectric actuators. The expenditure of the control forces is included in the objective function as a penalty term. The optimal control law for the micro-beam is derived using a maximum principle developed by Sloss et al. [J.M. Sloss, J.C. Bruch Jr., I.S. Sadek, S. Adali, Maximum principle for optimal boundary control of vibrating structures with applications to beams, Dynamics and Control: An International Journal 8 (1998) 355–375; J.M. Sloss, I.S. Sadek, J.C. Bruch Jr., S. Adali, Optimal control of structural dynamic systems in one space dimension using a maximum principle, Journal of Vibration and Control 11 (2005) 245–261] for one-dimensional structures where the control functions appear in the boundary conditions in the form of moments. The derived maximum principle involves a Hamiltonian expressed in terms of an adjoint variable as well as admissible control functions. The state and adjoint variables are linked by terminal conditions leading to a boundary-initial-terminal value problem. The explicit solution of the problem is developed for the micro-beam using eigenfunction expansions of the state and adjoint variables. The numerical results are given to assess the effectiveness and the capabilities of piezo actuation by means of moments to damp out the vibration of the micro-beam with a minimum level of voltage applied on the piezo actuators.     

Crystal structure of zdenekite NaPbCu5(AsO4)4Cl · 5H2O

The crystal structure of the mineral zdenekite NaPbCu₅(AsO₄)₄Cl · 5H₂O was established (Bruker SMART CCD diffractometer, synchrotron radiation, λ = 0.6843Å, R = 0.096 for 1356 reflections). Single-crystal X-ray diffraction study demonstrated that zdenekite belongs to the monoclinic system with the unit-cell parameters a = 10.023(7) Å, b = 19.55(1) Å, c = 10.023(6) Å, β = 90.02(1)°, sp. gr. P2₁/n, Z = 4. The structure consists of polyhedral layers parallel to the (010) plane. These layers are formed by Cu? polyhedra φ = O, Cl, H₂O) and AsO₄ tetrahedra. Distorted Na octahedra and Pb 7-vertex polyhedra and H₂O molecules coordinated to these metal atoms are located between the layers.     

Optimal control of a Timoshenko beam by distributed forces

The present paper considers the problem of optimally controlling the deflections and/or velocities of a damped Timoshenko beam subject to various types of boundary conditions by means of a distributed applied force and moment. An analytic solution is obtained by employing a maximum principle.     

Comparison of penalties resulting from first-order and all-order polarization mode dispersion distortions in optical fiber transmission systems

We compare the eye-opening penalty from a first-order polarization mode dispersion (PMD) model with that from an all-order PMD model in optical fiber transmission systems. Evaluating the performance by taking into account only first-order PMD produces a good approximation of the true eye-opening penalty of uncompensated systems when the penalty is low. However, when the penalties are high, this model overestimates the penalty for outage probabilities in the range of interest for systems designers, which is typically approximately 10(-5) to 10(-6).     

VARIATIONAL PRINCIPLES FOR NONLOCAL CONTINUUM MODEL OF ORTHOTROPIC GRAPHENE SHEETS EMBEDDED IN AN ELASTIC MEDIUM

Equations governing the vibrations and buckling of multilayered orthotropic graphene sheets can be expressed as a system of n partial differential equations where n refers to the number of sheets.This ...