Design, fabrication and analysis of micromachined high sensitivity and 0% cross-axis sensitivity capacitive accelerometers

This paper presents the design and fabrication of three MEMS based capacitive accelerometers. The first design illustrates the achievement of an accelerometer with 0% cross-axis sensitivity and has been fabricated using PolyMUMPs, a multi-user surface-micromachining process. A unidirectional parallel plate configuration is utilized in this design to illustrate the achievement of 0% cross-axis sensitivity and an acceptable performance range. In addition, a method is introduced to improve the sensitivity of a capacitive sensor employing a transverse configuration based on the relationship of initial gaps setup in comb-finger arrangements. A design based on this technique and the PolyMUMPs fabrication process is illustrated which demonstrates a sensitivity value of 4.07 fF/μm, with a nonlinearity of 2.05% for a ±3 μm sensor operating range. The last design based on this method and the SOIMUMPs fabrication process exhibits a sensitivity of 3.45 pF/μm for ±1 μm operating range of the sensor.     

Critical rotational speed,critical velocity of fluid flow and free vibration analysis of a spinning SWCNT conveying viscous fluid

In this article, the influences of rotational speed and velocity of viscous fluid flow on free vibration behavior of spinning single-walled carbon nanotubes (SWCNTs) are investigated using the modified couple stress theory (MCST). Taking attention to the first-order shear deformation theory, the modeled rotating SWCNT and its equations of motion are derived using Hamilton’s principle. The formulations include Coriolis, centrifugal and initial hoop tension effects due to rotation of the SWCNT. This system is conveying viscous fluid, and the related force is calculated by modified Navier–Stokes relation considering slip boundary condition and Knudsen number. The accuracy of the presented model is validated with some cases in the literatures. Novelty of this study is considering the effects of spinning, conveying viscous flow and MCST in addition to considering the various boundary conditions of the SWCNT. Generalized differential quadrature method is used to approximately discretize the model and to approximate the equations of motion. Then, influence of material length scale parameter, velocity of viscous fluid flow, angular velocity, length, length-to-radius ratio, radius-to-thickness ratio and boundary conditions on critical speed, critical velocity and natural frequency of the rotating SWCNT conveying viscous fluid flow are investigated.     

A numerical framework for load identification and regularization with application to rolling disc problem

Indirect identification methods are applied when direct measurement is unfeasible. One example is the measurement of the contact force between wheel and rail in railway traffic. This paper focuses on optimization-based methods for the identification of contact forces with the aim of developing a reliable and robust load identification scheme. A particular issue discussed here is the choice of discretization in space–time, enabling the sampling instances of the measurements, the parameterization of the sought input and the discretization of the pertinent state equations to be decoupled, in contrast to traditional methods such as, e.g. dynamic programming.In the present preliminary study where a 2-D disc is considered as a representative of a train wheel, a radial concentrated force rotates around the disc’s perimeter, representing the contact force acting on the rim of the wheel, while radial strains are measured on a set of points corresponding to the strain gauges position. The strain history data is then used in the identification procedure where the applied force is sought to minimize the discrepancy between the predicted and measured strain history. In particular the convergence of the results with respect to the temporal discretization of the model and the time parameterization of the sought loading history are investigated under the influence of noise. It is seen that choosing a discretization of the sought load that is coarser than that of the state variable gives a more robust scheme. The traditional Tikhonov regularization can also be added within the current framework. Furthermore, with the aid of a sensitivity analysis, the influence of measurement noise can be quantified.     

Finite-element analysis for magnetic resonance image artifact evaluation

The static magnetic field of a magnetic resonance imaging scanner can be distorted by the presence of materials, perturbing the spatial encoding process in magnetic resonance imaging and often resulting in image artifacts. The relationship between the image artifact size and magnetic susceptibility of the material specimen is of interest to engineers for the design of devices that are to be compatible with the imaging volume of the scanner. In this study, a finite-element method was used to simulate the distorted magnetic field of samples with different susceptibilities. With the knowledge of the external- and self- magnetic field interactions, a Lorentz correction was applied to compute the magnetic field deviation. The simulated results were then validated by the corresponding experimental magnetic resonance images.     

Modeling and Management of Firewall Policies

Firewalls are core elements in network security. However, managing firewall rules, especially for enterprise networks, has become complex and error-prone. Firewall filtering rules have to be carefully written and organized in order to correctly implement the security policy. In addition, inserting or modifying a filtering rule requires thorough analysis of the relationship between this rule and other rules in order to determine the proper order of this rule and commit the updates. In this paper we present a set of techniques and algorithms that provide automatic discovery of firewall policy anomalies to reveal rule conflicts and potential problems in legacy firewalls, and anomaly-free policy editing for rule insertion, removal, and modification. This is implemented in a user-friendly tool called ?Firewall Policy Advisor.? The Firewall Policy Advisor significantly simplifies the management of any generic firewall policy written as filtering rules, while minimizing network vulnerability due to firewall rule misconfiguration.     

Experimental investigation of the flow-induced motion of a square-section cylinder

The flow-induced motion(FIM)of an elastically mounted square-section cylinder is experimentally investigated over a wide range of Reynolds numbers(1.5×104＜Re＜7....     

Adsorption of U(Ⅵ) from acid solution on a low-cost sorbent:equilibrium,kinetic, and thermodynamic assessments

In this paper, waste clay was cured with ethyl acetate to obtain treated clay(TC), which was modified with gallic acid to obtain a low-cost sorbent that was characterized by EDX, SEM, and FTIR analysis. Uranium(Ⅵ) adsorption was achieved using the batch adsorption method on the TC and gallic acid-modified treated clay(GMTC). The maximum uptakes of U(Ⅵ) on TC and GMTC were 37.2 and 193.0 mg/g, respectively.The U(Ⅵ) adsorption kinetics on the TC and GMTC sorbents were well-fitted by the pseudo-second-order mechanism, and the adsorption equilibrium followed the Langmuir model. The optimum parameters were applied to El Sela leach solution for uranium recovery.     

Simple and sensitive method for the determination of trace amounts of thorium using a benzoquinone derivative

A novel simple, sensitive, rapid, direct, and spectrophotometry-based procedure was investigated to determine Th(IV) at trace amounts. The new method is based on Th(IV) chelation with 3,6-dichloro-2,5-dihydroxy-l,4-benzoquinone(DDBQ). The reagent reacts with Th(IV) in 0.1 M HCl to form an orange 1:2 complex. The stability constant value is 6.62×10~4 for the Th(IV)complex. The Th(IV)-DDBQ obtained shows one peak with a maximum at about 346 nm. The chelate forms immediately and the absorbance remains stable for over24 h. Beer's law was obeyed in the concentration range0–10 μg mL~(-1). The molar absorptivity and Sandell's sensitivity were 4.4×10~4 L mol~(-1)cm~(-1) and 0.0053 μg cm~(-2), respectively. Different analytical parameters were tested in detail. Interfering ion(cations and anions) effects were tested. Methods for Th(IV) determination by second and third-derivative spectrophotometry were also introduced at about 344 and 341 nm, respectively. These two derivative orders offer the feature of sensitivity without the necessity for solvent extraction,heating, or pre-concentration steps. Finally, the methods were successfully utilized for Th(IV) determination in monazite, environmental water, and wastewater samples.