Forced and self-excited oscillations of an optomechanical cavity

We experimentally study forced and self oscillations of an optomechanical cavity which is formed between a fiber Bragg grating that serves as a static mirror and between a freely suspended metallic mechanical resonator that serves as a moving mirror. In the domain of small amplitude mechanical oscillations, we find that the optomechanical coupling is manifested as changes in the effective resonance frequency, damping rate and cubic nonlinearity of the mechanical resonator. Moreover, self oscillations of the micromechanical mirror are observed above a certain optical power threshold. A comparison between the experimental results and a theoretical model that we have recently presented yields a good agreement. The comparison also indicates that the dominant optomechanical coupling mechanism is the heating of the metallic mirror due to optical absorption.Comment: 11 pages, 6 figure

Optimization of sensor design for Barkhausen noise measurement using finite element analysis

The effects of design parameters for optimizing the performance of sensors for magneticBarkhausen emission measurement are presented. This study was performed using finite element analysis. The design parameters investigated include core material, core-tip curvature, core length, and pole spacing. Considering a combination of permeability and saturation magnetization, iron was selected as the core material among other materials investigated. Although a flat core-tip would result in higher magnetic flux concentration in the test specimen, a curved core-tip is preferred. The sensor-to-specimen coupling is thereby improved especially for materials with different surface geometries. Smaller pole spacing resulted in higher flux concentration

Modeling transport through single-molecule junctions

Non-equilibrium Green's functions (NEGF) formalism combined with extended Huckel (EHT) and charging model are used to study electrical conduction through single-molecule junctions. Analyzed molecular complex is composed of asymmetric 1,4-Bis((2'-para-mercaptophenyl)-ethinyl)-2-acetyl-amino-5-nitro-benzene molecule symmetrically coupled to two gold electrodes [Reichert et al., Phys. Rev. Lett. Vol.88 (2002), pp. 176804]. Owing to this model, the accurate values of the current flowing through such junction can be obtained by utilizing basic fundamentals and coherently deriving model parameters. Furthermore, the influence of the charging effect on the transport characteristics is emphasized. In particular, charging-induced reduction of conductance gap, charging-induced rectification effect and charging-generated negative value of the second derivative of the current with respect to voltage are observed and examined for molecular complex.Comment: 8 pages, 3 figure

Real-time performance of mechatronic PZT module using active vibration feedback control

This paper proposes an innovative mechatronic piezo-actuated module to control vibrations in modern machine tools. Vibrations represent one of the main issues that seriously compromise the quality of the workpiece. The active vibration control (AVC) device is composed of a host part integrated with sensors and actuators synchronized by a regulator; it is able to make a self-assessment and adjust to alterations in the environment. In particular, an innovative smart actuator has been designed and developed to satisfy machining requirements during active vibration control. This study presents the mechatronic model based on the kinematic and dynamic analysis of the AVC device. To ensure a real time performance, a H2-LQG controller has been developed and validated by simulations involving a machine tool, PZT actuator and controller models. The Hardware in the Loop (HIL) architecture is adopted to control and attenuate the vibrations. A set of experimental tests has been performed to validate the AVC module on a commercial machine tool. The feasibility of the real time vibration damping is demonstrated and the simulation accuracy is evaluate

An Integrated Multidisciplinary Nanoscience Concentration Certificate Program for STEM Education

Integration of nanoscience and nanotechnology curricula into the College of Science, Mathematics, and Technology (CSMT) at the University of Texas at Brownsville (UTB) is reported. The rationale for the established multidisciplinary Nanoscience Concentration Certificate Program (NCCP) is to: (i) develop nanotechnology-relevant courses within a comprehensive Science, Engineering and Technology curriculum, and, to offer students an opportunity to graduate with a certificate in nanoscience and nanotechnology; (ii) to contribute to students\u27 success in achieving student outcomes across all college\u27s majors, and, improve the breath, depth and quality of science, technology, engineering and mathematics (STEM) graduates\u27 education; (iii) through NCCP, recruit certificate- and associate-degree seeking students into four year programs in engineering and physical sciences. A long-term goal is to develop an ABET accredited bachelor program in nanoscience. This program is expected to reach out to a large group of undergraduate students in a coordinated manner, enhance students\u27 knowledge and skills, as well as facilitate efforts of individual faculty members in STEM education. The UTB NCCP is supported by the NSF NUE program, under which we are developing and offering seven upper-level interdisciplinary undergraduate courses. These courses and program are assessed and evaluated

Molecular Momentum Transport at Fluid-Solid Interfaces in MEMS/NEMS: A Review

This review is focused on molecular momentum transport at fluid-solid interfaces mainly related to microfluidics and nanofluidics in micro-/nano-electro-mechanical systems (MEMS/NEMS). This broad subject covers molecular dynamics behaviors, boundary conditions, molecular momentum accommodations, theoretical and phenomenological models in terms of gas-solid and liquid-solid interfaces affected by various physical factors, such as fluid and solid species, surface roughness, surface patterns, wettability, temperature, pressure, fluid viscosity and polarity. This review offers an overview of the major achievements, including experiments, theories and molecular dynamics simulations, in the field with particular emphasis on the effects on microfluidics and nanofluidics in nanoscience and nanotechnology. In Section 1 we present a brief introduction on the backgrounds, history and concepts. Sections 2 and 3 are focused on molecular momentum transport at gas-solid and liquid-solid interfaces, respectively. Summary and conclusions are finally presented in Section 4