The influence of fiber orientation on electromagnetic shielding in liquid-crystal polymers

The influence of conductive carbon-fiber orientation and weight percentage on the electromagnetic (EM) shielding effectiveness (SE) in liquid-crystal polymer (LCP) composites was investigated experimentally and theoretically. The experimental results show that the SE of LCP composites with longitudinal fiber orientation is higher than random fiber orientation under the same weight percentage of carbon fibers filled. This is because longitudinal fiber orientation is parallel to the electric field of the incident EM wave, and most of the energy of the incident wave is reflected by the longitudinal fiber. In comparison with nylon66 composites, the SEs of LCP composites with longitudinal fiber orientation are also higher than nylon66 composites with the same content of carbon fibers. Furthermore, the SE of 20% conductive carbon-fiber-filled LCP composites was measured to be 50 dB at a frequency of 0.3 GHz and 53 dB at 1 GHz, which is at least 10 dB higher than that of nylon66 composites. The SE predicted by theoretical models and measured by experiments was in good agreement for carbon-fiber-filled LCP composites of longitudinal and random fiber orientations.     

High Electromagnetic Shielding of a 2.5-Gbps Plastic Transceiver Module Using Dispersive Multiwall Carbon Nanotubes

A novel polyimide film, consisting of finely dispersed multiwall carbon nanotubes (MWCNTs) in an ionic liquid (IL), is demonstrated to be high shielding effectiveness (SE) for use in packaging a 2.5-Gbps plastic transceiver module. The IL-dispersed MWCNT composite exhibits a high SE of 40 ~ 46 dB. By comparison, the composite fabricated by nondispersive process requires a higher loading of MWCNTs at 50 wt- % than the IL-dispersed process at only 30 wt-%. The electromagnetic susceptibility (EMS) performance is experimentally evaluated by the eye diagram and bit-error-rate for a 2.5-Gbps lightwave transmission system. The package housing fabricated by the dispersive MWCNT composites shows an enhanced EMS performance, an improved mask margin, and a lower-power penalty. These results indicate that the IL-dispersed MWCNT composites are suitable for packaging low-cost and high-performance optical transceiver modules used in the fiber to the home lightwave transmission systems.     

Bidirectional Transmission Using Tunable Fiber Lasers and Injection-Locked Fabry–PÉrot Laser Diodes for WDM Access Networks

We propose and demonstrate the use of fiber ring lasers and Fabry-Perot laser diodes (FP-LDs) for wavelength-division-multiplexing access networks. The fiber ring laser not only generates downstream data traffic but also serves as the wavelength-selecting injection light source for the FP-LD located at the subscriber site. Moreover, it is wavelength tunable and can be applied to dynamic wavelength assignment networks. The ring laser has a tunable range of 30 nm in the C-band and a power fluctuation smaller than 0.6 dB. For 10-Gb/s downstream and 1.25-Gb/s upstream transmissions over 10-km single-mode fiber, power penalties less than 0.9 and 0.5 dB are demonstrated, respectively. A 40-dB sidemode suppression ratio is obtained for the FP-LD injection-locking at 1544.8 nm.     

Evaluation of Four Tree Algorithms in Predicting and Investigating the Changes in Aquifer Depth

One of the key elements in improved management and better planning for aquifer maintenance is the ability to predict changes in aquifer depth. In order to forecast changes in aquifer depth in Qazvin plain, four methods, including Classification and Regression Tree (CART), Reduced Error Pruning Trees (RepTree), M5-Pruned (M5P), and M5Rule, were used in this work. The absolute mean error (MAE) and coefficient of determination (R2) data show that the CART algorithm performs better than other algorithms at forecasting changes in aquifer depth. The CART algorithm's prediction findings showed that the aquifer's behavior in the two seasons was entirely different. In the first stage, which began in November and continued through April, there was an annual average depth of 0.045 m. The aquifer depth has been greatly influenced by rising precipitation and falling air temperature. The aquifer experiences an average decline of 0.15 m in the second portion, which runs from May to October. Aquifer depth has significantly decreased as a result of declining natural water supplies and rising agricultural water use. It is advised to utilize a crop scheme with reduced water need when rainfall reduces due to the strong effect of changes in aquifer depth from rainfall with a delay of one to three months ago.

     

Effect of blending sodium polyethylene‐5‐sulfoisophthalate on adhesion of clinical bacteria on polyethylene terephthalate

This work studies the adhesion of clinical infecting bacteria, S. aureus and E. coli, on prosthetic polymeric materials. Membranes were prepared from polyethylene terephthalate (PET) blending at various ratios with sodium polyethylene‐5‐sulfoisophthalate (SPES). The membranes were characterized by measuring the contact angle, equilibrium water content, and the surface concentration of sodium sulfonate. The results show that sulfonate makes the membrane more hydrophilic. The surface properties of bacteria were determined by measuring the adhesion to n‐octane (B%) and the contact angles to water and α‐bromonaphthalene. For the four bacteria studied, encapsulated S. aureus was the most hydrophobic and had the highest amount of bacteria attached to the surface of SPES/PET membrane. Furthermore, the attached amount decreased with the increase of the content of SPES. Empirical correlations for predicting the attached amount from the surface properties of both polymer and bacteria were obtained from linear regression. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91: 3587–3594, 2004     

New DC Hybrid Filter for Attenuating Low-Frequency Ripple of AC-DC Power Converter

In this article, a new DC hybrid power filter is proposed to attenuate the low–frequency ripple of AC-DC power converter. The proposed DC hybrid power filter is connected between the DC bus of AC-DC power converter and the load, and it composes of a passive power filter and a single-arm power converter. The passive power filter can reduce the voltage rating of single-arm power converter, and the operation of single-arm power converter generates a virtual harmonic resistor connected to the load in series. The DC hybrid power filter can suppress the twice-utility-frequency ripple for eliminating the use of electrolytic capacitor. The salient feature is that the control circuit of the proposed DC hybrid power filter is simplified because only a feedforward control is used. A hardware prototype is developed to validate the performance of the proposed DC hybrid power filter. The experimental results are as expected.     

Two-dimensional flows in gas hydrostatic bearings in thin films of variable thickness analysed by finite element method

For a two-dimensional gas flow in a thin film of variable thickness, hydrostatic pressure can be calculated using finite element methods. The load variations related to the bearing configurations and the operating conditions are investigated. Spherical and conical hydrostatic bearings with gas pockets are analysed with constant pressure in the pocket inlet as the boundary condition. The variation of load-carrying capacity with various eccentricities is investigated. The valid regimes that produce normal bearing performance are obtained through the necessary restrictions on the related parameters.     

Efficient and fast iterative reweighted least-squares nonrecursivefilters

An efficient and fast technique for designing L_p approximation filters using the iterative reweighted least-squares (IRLS) algorithm is proposed. This technique introduces an extra frequency response which implicitly includes the weighting function such that the filter coefficients can be obtained with O(N²) complexity     

The solubility of methane in aqueous solutions of monoethanolamine,diethanolamine and triethanolamine

The solubility of methane in 3 kmol/m³ solutions of monoethanolamine, diethanolamine, and triethanolamine was measured from 25° to 125°C and pressures up to about 13 MPa. Measurements were also made for the solubility of methane in water at 25° to 125°C and pressures up to 18 MPa in order to confirm the accuracy of the experimental technique. It is demonstrated that methane is more soluble (in terms of mole fraction) in the amine solution than in pure water. Furthermore, the solubility is an increasing function of the size of the alkanolamine. The solubility data were modeled using a Henry's-law approach and the results summarized in terms of salting-in coefficients.     

Active islanding detection method for the grid-connected photovoltaic generation system

This paper proposes an active islanding detection method incorporated into the control of the grid-connected inverter to protect the photovoltaic generation system from the islanding operation. The proposed active islanding detection method performs the grid-connected inverter as a virtual resistor with the operation frequency slightly higher or lower than the fundamental frequency of the utility voltage. The function of virtual resistor will not be actuated when the utility is nominal, and the grid-connected inverter can convert the DC power from the solar array to an AC power. When the strong utility is lost, the grid-connected inverter acts as a virtual resistor with the operation frequency slightly higher or lower than the fundamental frequency of the utility voltage. Thus, the frequency and the amplitude of the local load voltage will be away from their normal values under the islanding operation. Hence, the proposed active islanding detection method can immediately detect the islanding operation. A prototype is developed and tested to demonstrate the performance of the proposed active detection method. Both computer simulation and experimental results verify that the performance of the proposed active islanding detection method is expected.