Luminous, fully aliphatic polyamides: Multicolor photoluminescence, their pH and solvent dependency

Novel luminous aliphatic polyamides were obtained from a condensation reaction of ethylene diamines and malonyl dichloride in the presence of triethylamine. These polymers appeared in blackish red and reddish orange solids and unusually exhibited a visible light-emission. Their fluorescence properties were significantly dependent on the excitation wavelength, media polarity, and acidity. These polymers emitted fairly strong visible lights in a wide range from blue to near yellow when excited at wavelengths longer than 305 nm. The emission bands significantly shifted to longer wavelengths during the increase in the polarity of the solvent used. Their fluorescence intensities significantly increased under acidic conditions.     

Orthotropic strain rate potential for the description of anisotropy in tension and compression of metals

In this paper, a macroscopic anisotropic strain rate potential, which can describe both the anisotropy and tension-compression asymmetry of the plastic response of textured metals is derived. This strain rate potential is the exact work-conjugate of the anisotropic stress potential CPB06 of Cazacu et al. (2006). Application of the developed strain rate potential to HCP high-purity alpha-titanium is presented.     

A New Architecture of Matched Filter for Chirp Spread Spectrum in IEEE 802.15.4a

We propose a new matched filter architecture for chirp spread spectrum in IEEE 802.15.4a. By using relations among the four subchirps, the proposed architecture comprises four subfilters utilizing only a set of coefficients matched to the first subchirp. The four subfilters share adders and registers, and as a result, the required adders and registers for implementation are reduced.     

Fully-integrated wideband CMOS VCO with improved f–V linearity and low tuning sensitivity

A technique to improve the linearity of the frequency-voltage (f - V) characteristic and to reduce the differential tuning sensitivity, KVCO, of voltage-controlled oscillators (VCOs) is proposed. The VCO designed using the linearisation technique is tunable from 806 to 1113 MHz with a 34 tuning range and exhibits a nearly constant KVCO of 62 MHz/V over the entire frequency range.     

A pseudo-random asynchronous duty cycle MAC protocol in wireless sensor networks

We propose a pseudo-random asynchronous duty cycle MAC protocol in wireless sensor networks. The proposed protocol adopts a hash function to determine the next wake-up times. As the next wake-up times are known in advance, the sensor nodes do not need to remain active until their intended receivers wake up. Given an end-to-end delay requirement, the proposed protocol significantly decreases energy consumption by reducing the idle listening time.     

Nano-sized patterns derived from a SiCN preceramic polymer: Fabrication and their characterization

A microfabrication of ceramic materials with a low shrinkage has created inevitable demands in the fields of micro total analysis systems (μ-TAS) and microfluidic devices with thermal, chemical, and mechanical stability. In this study, nano-sized patterns were prepared using a soft lithographic technique, followed by the UV and thermal curation of a non-oxide SiCN preceramic polymer. The characterization of the thermal and mechanical properties of the cured preceramic polymer revealed that it becomes ceramic-like after the heat treatment at higher temperature than 600 °C. The heat-treated nano-sized patterns showed a low linear shrinkage as well as good chemical stability and optical properties. The results showed the feasibility of enormous potentials of the cured preceramic polymer because of the low shrinkage, the high optical transparency, and the thermal and chemical stability.     

Effect of stereosequences on crystallinity and properties of zone‐drawn poly(vinyl alcohol) microfibrils

To effectively orient the molecular chains of novel syndiotactic poly(vinyl alcohol) (PVA) microfibrillar fiber (PVA fibril), a high‐temperature zone‐drawing method was adopted. The PVA fibrils were directly prepared from the saponification and in situ fibrillation without a spinning procedure. The maximum draw ratio of the PVA fibril increased with a decrease in the syndiotactic diad (r‐diad) content, indicating that the deformability of PVA molecules was lowered in higher syndiotactic PVA. Degree of crystal orientations up to 0.990 were achieved by stretching the PVA fibril with the r‐diad content of 65.1% and the original degree of crystal orientation of 0.902 at 250 °C close to its crystal melting temperature (T_m). When the same draw ratio was applied to the fibrils, a higher crystal orientation was achieved for the fibrils having higher syndiotacticity. Wide‐angle X‐ray data show that the longitudinal crystal sizes of drawn PVA fibrils were larger in higher syndiotacticities. The degree of crystal orientation, crystallinity, T_m, longitudinal crystal size, and tensile strength of the maximum drawn PVA fibril with a r‐diad content of 65.1% were 0.99, 0.97, 279 °C, 187 Å, and 4.66 N/tex, respectively. © 2001 John Wiley & Sons, Inc. J Polym Sci Part B: Polym Phys 39: 1263–1271, 2001     

60-GHz CPW-fed post-supported patch antenna using micromachining technology

A 60-GHz coplanar waveguide (CPW)-fed post-supported patch antenna is presented using micromachining technology. In the proposed structure, the radiating patch and the feed line network can be optimized separately with a substrate. The antenna performance is improved by elevating the patch in the air. A patch array antenna is also designed with a simple feed network. The fabricated antenna shows broad band characteristics such as -10 dB bandwidth of 4.3GHz from 58.7GHz to 64.5GHz in the single patch antenna and 8.7GHz from 56.3GHz to 65GHz in 2/spl times/1 patch array antenna.     

An electrically modifiable synapse array composed ofmetal-ferroelectric-semiconductor (MFS) FET's using SrBi2Ta2O9 thin films

An array of metal-ferroelectric-semiconductor field effect transistors (MFSFETs) is fabricated on a silicon-on-insulator (SOI) structure using SrBi₂Ta₂O₉ as the gate insulator. It is demonstrated that each FET shows good characteristics as a nonvolatile analog memory due to partial polarization of the SrBi ₂Ta₂O₉ film and that the array operates as an electrically modifiable synapse circuit for carrying out the weighted sum operation in an artificial neural network