Stability and resonance of micro-machined gyroscope under nonlinearity effects

Resonance frequency for a micro-gyroscope plays an extremely significant role since the driving frequency is accordingly tuned so that the best sensitivity and resolution can be achieved. In practice, the micro-gyroscope is usually driven into resonance to retain its superior angular rate detection capability. However, the embedded nonlinearity effect upon the micro-gyroscopic dynamics may not only deteriorate the stability around the vicinity of operation point, but also alter the initially-designed resonance frequencies so that the angular rate detection performance of the micro-gyroscope is dramatically degraded. Hence, the nonlinearities, mainly resulting from flexure springs and electrostatic force, are both taken into account to construct the nonlinear dynamic model of the micro-gyroscope in our work at first. Secondly, the instability region of the proposed micro-gyroscope under different driving frequency and natural frequencies, which tends to be drifted due to mechanical fatigue and temperature rise, is unveiled. In order to catch the insight of slight variation of system parameters, the nonlinear dynamic equation is analyzed by using multiple scales method to outstand the influence of the variation of driving moment. Thirdly, the external resonance and non-resonant hard excitation of the micro-gyroscope—totally five types—are both theoretically studied. It is interesting to find that the resonance frequencies and resonant magnitude are both changed accordingly if either the driving frequency or the magnitude of driving moment is tuned via control loop for the sake of considering more stability or better performance. Finally, the chaotic behavior of the micro-gyroscope is numerically inspected by bifurcation diagrams and verified that the sense mode and drive mode have the similar orbits for transitions across distinct patterns of dynamic motion of the presented micro-gyroscope.     

Correlation between chain segment and ion mobility in an epoxy resin system. A free volume analysis

Steady shear viscosity and ionic conductivity have been measured for nine commercial diglycidyl ether of bisphenol-A (DGEBA) epoxy resins with molecular weights ranging from 340 to 14,200. The temperature dependence of viscosity and ionic conductivity was modeled using free volume viscosity and ionic conductivity relationships, which correlate the fractional free volume required for polymer chain segment motion (B) and the fractional free volume required for ion motion (B′) with polymer structure. The fractional free volume required for polymer chain segment mobility was observed to increase systematically with the molecular weight of the resins. The fractional free volume required for ion mobility did not vary for the resin series. A stoichiometric mixture of a low molecular weight DGEBA resin and a 4,4′-diaminodiphenyl sulfone cross-linker was partially polymerized to extents of reaction ranging from 0% to 49%. The fractional free volume required for polymer segment mobility for these partially polymerized samples was consistent with results for the neat resins. © 1993 John Wiley & Sons, Inc.     

A new phlorotannin from the brown alga Ecklonia stolonifera

A new phlorotannin, named eckstolonol (1), was isolated from the EtOAc soluble fraction of the methanolic extract of the brown alga, Ecklonia stolonifera OKAMURA, along with three known phlorotannins, eckol (2), phlorofucofuroeckol A (3), and dieckol (4). The structure of eckstolonol was identified as 5,8,13,14-tetraoxa-pentaphene-1,3,6,9,11-pentaol on the basis of spectroscopic evidence. The new compound was found to be a radical scavenger on the 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical.     

MR safety and compatibility of a noninvasively expandable total-joint endoprosthesis

A noninvasively expandable total-joint endoprosthesis is now available for pediatric patients; the prosthesis can be lengthened by external application of a magnetic field. We investigated the risks of unintentional heating or lengthening of the prosthesis during MR imaging and evaluated the effect of the device on the diagnostic efficacy of MR imaging of surrounding tissues. We performed MR imaging at 1.5 T by using standard pulse sequences and pulse sequences with high-gradient and high-radiofrequency duty cycle. MR imaging caused no measurable change in prosthesis length, and the temperature of the prosthesis increased by less than 1 degrees C during repeated 14-min exposures. Despite significant signal loss and image distortion around the prosthetic joint, clinically useful images were obtained as close as 12 cm from the ends of the prosthetic stems, measured toward the body of the device. Thus, the prosthesis can be safely exposed to MR imaging pulse sequences at 1.5 T, and the visualization of some tissue surrounding the device is clinically useful.     

Morphological characterization of nylon‐6 nanocomposite following a large‐scale simple shear process

A commercial grade nylon‐6/clay nanocomposite (from Ube industries) is subjected to a large‐scale simple shear orientation process and the resulting morphology is investigated. Both the orientation and aspect ratio of nanoclays, which can be altered by the simple shear process, are studied. The incorporation of well‐dispersed nanoclays into the nylon matrix greatly reduces the nylon chain mobility as well as the percent crystallinity. Two types of lamellar orientation have been found, as revealed by small‐angle X‐ray scattering. One type of lamellae is oriented ～41° away from the clay surface, whereas the simple shear process induces another weakly preferred lamellar orientation nearly perpendicular to the clay surface. The formation of the above lamellar orientations appears to be related to both orientation of the clay in the nanocomposite and the simple shear process. The possible molecular mechanisms leading to the final morphology of the nylon‐6/clay nanocomposite is discussed. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3555–3566, 2005     

Using hierarchical self-assembly to form three-dimensional lattices of spheres

This paper describes an approach to the fabrication of three-dimensional (3-D) structures of millimeter-scale spherical beads having a range of lattices-tetragonal, cubic, and hexagonal-using hierarchical self-assembly. The process has five steps: (i) metal-coated beads are packed in a rod-shaped cavity in an elastomeric polymer (poly(dimethylsiloxane), PDMS); (ii) the beads are embedded in a second polymer (PDMS or polyurethane, PU) using a procedure that leaves the parts of the beads in contact with the PDMS exposed; (iii) the exposed areas of the beads are coated with a solder having a low melting point; (iv) the polymer rods-with embedded beads and exposed solder drops-are suspended in an approximately isodense medium (an aqueous solution of KBr) and allowed to self-assemble by capillary interactions between the drops of molten solder; and (v) the assembly is finished by several procedures, including removing the beads from the polymer matrix by dissolution, filling the voids left with another material, and dissolving the matrix. The confinement of the beads in regular structures in polymer rods makes it possible to generate self-assembled structures with a variety of 3-D lattices; the type of the lattice formed can be controlled by varying the size of the beads, and the size and shape of the cross-section of the rods.     

Dissections: self-assembled aggregates that spontaneously reconfigure their structures when their environment changes

This Communication describes a new strategy for the design of adaptive structures based on reconfigurable mesoscale self-assembly. Several sets of millimeter-scale objects have been designed that can self-assemble into two different, regular aggregates at the interface between an aqueous solution and perfluorodecalin; the choice between the two aggregates is determined by the density of the aqueous phase.