Liquid‐crystalline behavior of chitosan in malic acid

This report describes how the degree of deacetylation and molecular weight of chitosan and the concentrations of sodium chloride and malic acid affect the formation of lyotropic chitosan liquid crystals. Chitosan samples of various degrees of deacetylation were prepared from β‐chitin that was isolated from squid pens. They were degraded by ultrasonic irradiation to various molecular weights. The critical concentrations forming chitosan liquid crystals were determined with a polarized microscope. A chitosan sample with a degree of deacetylation of 67.2–83.6% formed cholesteric lyotropic liquid crystals when it was dissolved in 0.37–2.59M malic acid. The critical concentrations increased with increasing degrees of deacetylation of chitosan. They decreased with increasing molecular weights or increasing concentrations of sodium chloride and malic acid. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

Digital spectra of nonuniformly sampled signals: a robust samplingtime offset estimation algorithm for ultra high-speed waveformdigitizers using interleaving

The author presents an algorithm for estimating the sampling time offsets encountered at the parallel sampling paths of an ultra-high-speed waveform digitizing system which is realized by interleaving many sample-hold and A/D (analog/digital) converter modules. One obvious application of this algorithm is to feed these estimates back to adjustable delay units in all the sampling paths to compensate the sampling-time offsets. Simulation results indicate that with an 8-bit quantizer the residual timing error can be reduced to just about 0.05% of the sampling period     

Improved results for neutral systems with nonlinear perturbations

Abstract

In this paper, a simple robust stability problem for uncertain neutral systems is considered. The uncertainty under consideration is nonlinear parameter perturbations and does not require a matching condition. Based on the constructive use of the Lyapunov functional approach and linear matrix inequality (LMI) technique, a new delay‐dependent criterion is proposed to guarantee robust stability for such systems. Finally, less conservative than previous results are illustrated by the five examples.     

Physical and chemical composition of hospital waste

A knife cut injuring the meninges and the upper layers of rat neocortex transiently increases the levels of preprocholecystokinin-mRNA in the whole ipsilateral cortex. 48 h after the injury, the rise in gene expression was reduced by the edema-induced increase in tissue pressure which develops after the trauma. The beta-adrenoceptor antagonists alprenolol (4 mg/kg) and propranolol (1 mg/kg), given i.m. 30 min prior to the injury, reduced the increase by 75.6 and 100%, respectively. In contrast, blockade of alpha-adrenoceptors as well as of dopamine and serotonin receptors by respective antagonists did not affect the injury-induced increase in levels of preprocholecystokinin-mRNA. These results suggest that noradrenergic neurons can contribute via stimulation of beta-adrenoceptors to the initiation of the injury-induced increase in preprocholecystokinin gene expression.     

STABILITY CRITERIA FOR A CLASS OF NEUTRAL SYSTEMS VIA THE LMI APPROACH

In this paper, the asymptotic stability for a class of neutral systems with multiple discrete and distributed time delays is investigated. The Lyapunov stability theory is applied to guarantee the stability of the systems. The linear matrix inequality (LMI) approach is used to improve our results. By means of some mathematical analysis, the presented conditions are proved to be less conservative and flexible than some recent reports. A numerical example is given to illustrate the use of our results.     

On delay‐dependent LMI‐based guaranteed cost control of uncertain neutral systems with discrete and distributed time‐varying delays

In this paper, the problem of designing robust guaranteed cost control law for a class of uncertain neutral system with a given quadratic cost function is considered. Based on Lyapunov–Krasovskii functional theory, a delay‐dependent criterion for the existence of guaranteed cost controller is expressed in the form of two linear matrix inequalities (LMIs), which can be solved by using effective LMI toolbox. Moreover, a convex optimization problem satisfying some LMI constraints is formulated to solve a guaranteed cost controller which achieves the minimization of the closed‐loop guaranteed cost. An efficient approach is proposed to design the guaranteed cost control for uncertain neutral systems. Computer software Matlab can be used to solve all the proposed results. Finally, a numerical example is illustrated to show the usefulness of our obtained design method. Copyright © 2006 John Wiley & Sons, Ltd.     

Design of a compact dual-mode ring resonator bandpass filter with harmonic suppression

Abstract

An approach to suppress the harmonic responses in a dual-mode circular ring resonator bandpass filter is presented. Feed lines with one-sided coupling arms are suitably relocated around the ring resonator to introduce phase interference between two degenerate modes for simultaneously suppressing the second and third harmonics. Three open loop resonators at the rim of the ring are adopted to further suppress the second harmonic. By fabricating on a FR4 glass-epoxy base, this approach is demonstrated to have effectiveness in broadening the filter's rejection band in both simulations and measurements without affecting the fundamental response or increasing the device size.     

Dynamic analysis and grinding tracks in the magnetic fluid grinding system: Part II. The imperfection and ball interaction effects

To model the effects of the geometrical imperfections on the ball motion and its grinding track, it is therefore necessary to combine a dynamic model of the support system of balls with the previous model. For the geometrical imperfections on the ball, because of the interaction between the contact loads and the ball-spin speed, it causes the friction contact condition to remain at the interfaces with lower contact loads and lower ball-spin speeds in the separation case at the initial stage. Consequently, the variation in the ball-spin angle and the area covered by the grinding tracks is small. However, when the intermittent separation occurs at the geometrical imperfections on the ball orbit, it causes a large oscillation in the ball-spin angle and the ball-spin speed. Consequently, the effect of the imperfections in the ball orbit on the area covered by the grinding tracks is larger than that of the ball geometry. Ball–ball contacts cause a large oscillation in the ball-spin angle resulting in a uniform distribution of the grinding tracks. Hence, the effect of ball–ball contacts is one of the most important mechanisms in achieving a uniform distribution of the grinding tracks.     

Normal-Pressure Hot-Pressing of α-Alumina-Diamond Composites

α-Alumina-diamond composites have been developed by normal hot-pressing procedures using a conventional pressure of 32 MPa and 1250°C. Heretofore this type of composite has required a pressure of 6 GPa (60 kbar) to prevent the transformation of diamond to graphite. The mechanical properties, density, and thermal expansion coefficient of these composites have been characterized. The fracture toughness ( K _Ic) of alumina shows a considerable increase with the addition of diamond particles. Diamond additions tend to decrease the thermal expansion coefficient of these composites. The composite properties are dependent on the volume fraction of diamond particles.     

Boron Carbide Reinforced Alumina Composites

The mechanical properties of alumina have been successfully improved by adding isolated boron carbide particles of two different shapes. A K _Ic of 7.26 ± 0.20 MPa · m^1/2 for alumina—boron carbide whiskerlike composites and of 5.27 ± 0.12 MPa · m^1/2 alumina—boron carbide shardlike particle composites has been achieved. The fracture toughness of these composites is dependent on the volume fraction of the boron carbide particles as well as their size and shape. The flexural strength is also appreciably enhanced to a constant value with from 5 to 20 vol% boron carbide additions. The whiskerlike particles increase the flexural strength by 25% and the shardlike particles produce a 47% improvement.